Add mention of Merge request in Slack message

To make the message clearer.

app/models/project_services/chat_message/merge_message.rb

@@ -48,7 +48,7 @@ module ChatMessage
     end
 
     def merge_request_message
-      "#{user_combined_name} #{state_or_action_text} #{merge_request_link} in #{project_link}"
+      "#{user_combined_name} #{state_or_action_text} merge request #{merge_request_link} in #{project_link}"
     end
 
     def merge_request_link

changelogs/unreleased/21002-slack-opened-merge-request-webhook-message-is-malformed.yml

+---
+title: Add explicit mention of Merge request in Slack message
+merge_request: 33152
+author:
+type: changed

ee/spec/models/project_services/chat_message/merge_message_spec.rb

@@ -36,7 +36,7 @@ RSpec.describe ChatMessage::MergeMessage do
 
     it 'returns a message regarding completed approval of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User (test.user) approved <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
+        'Test User (test.user) approved merge request <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
         'in <http://somewhere.com|project_name>')
       expect(subject.attachments).to be_empty
     end
@@ -49,7 +49,7 @@ RSpec.describe ChatMessage::MergeMessage do
 
     it 'returns a message regarding revocation of completed approval of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User (test.user) unapproved <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
+        'Test User (test.user) unapproved merge request <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
         'in <http://somewhere.com|project_name>')
       expect(subject.attachments).to be_empty
     end
@@ -62,7 +62,7 @@ RSpec.describe ChatMessage::MergeMessage do
 
     it 'returns a message regarding added approval of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User (test.user) added their approval to <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
+        'Test User (test.user) added their approval to merge request <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
         'in <http://somewhere.com|project_name>')
       expect(subject.attachments).to be_empty
     end
@@ -75,7 +75,7 @@ RSpec.describe ChatMessage::MergeMessage do
 
     it 'returns a message regarding revoking approval of merge requests' do
       expect(subject.pretext).to eq(
-        'Test User (test.user) removed their approval from <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
+        'Test User (test.user) removed their approval from merge request <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> '\
         'in <http://somewhere.com|project_name>')
       expect(subject.attachments).to be_empty
     end

spec/models/project_services/chat_message/merge_message_spec.rb

@@ -52,7 +52,7 @@ describe ChatMessage::MergeMessage do
     context 'open' do
       it 'returns a message regarding opening of merge requests' do
         expect(subject.pretext).to eq(
-          'Test User (test.user) opened <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> in <http://somewhere.com|project_name>')
+          'Test User (test.user) opened merge request <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> in <http://somewhere.com|project_name>')
         expect(subject.attachments).to be_empty
       end
     end
@@ -63,7 +63,7 @@ describe ChatMessage::MergeMessage do
       end
       it 'returns a message regarding closing of merge requests' do
         expect(subject.pretext).to eq(
-          'Test User (test.user) closed <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> in <http://somewhere.com|project_name>')
+          'Test User (test.user) closed merge request <http://somewhere.com/-/merge_requests/100|!100 *Merge Request title*> in <http://somewhere.com|project_name>')
         expect(subject.attachments).to be_empty
       end
     end
@@ -77,7 +77,7 @@ describe ChatMessage::MergeMessage do
     context 'open' do
       it 'returns a message regarding opening of merge requests' do
         expect(subject.pretext).to eq(
-          'Test User (test.user) opened [!100 *Merge Request title*](http://somewhere.com/-/merge_requests/100) in [project_name](http://somewhere.com)')
+          'Test User (test.user) opened merge request [!100 *Merge Request title*](http://somewhere.com/-/merge_requests/100) in [project_name](http://somewhere.com)')
         expect(subject.attachments).to be_empty
         expect(subject.activity).to eq({
           title: 'Merge Request opened by Test User (test.user)',
@@ -95,7 +95,7 @@ describe ChatMessage::MergeMessage do
 
       it 'returns a message regarding closing of merge requests' do
         expect(subject.pretext).to eq(
-          'Test User (test.user) closed [!100 *Merge Request title*](http://somewhere.com/-/merge_requests/100) in [project_name](http://somewhere.com)')
+          'Test User (test.user) closed merge request [!100 *Merge Request title*](http://somewhere.com/-/merge_requests/100) in [project_name](http://somewhere.com)')
         expect(subject.attachments).to be_empty
         expect(subject.activity).to eq({
           title: 'Merge Request closed by Test User (test.user)',