Fix typo in issue confidentiality handling

When trying to make public an issue linked to a confidential epic,
the resulting banner message started with "Issue this issue...".
This MR corrects the typo.

Fixed: fixed typo

ee/app/models/ee/issue.rb

@@ -271,16 +271,16 @@ module EE
       return unless epic
 
       if !confidential? && epic.confidential?
-        errors.add :issue, confidentiality_error
+        errors.add :base, confidentiality_error
       end
     end
 
     def confidentiality_error
       if changed_attribute_names_to_save.include?('confidential')
-        return _('this issue cannot be made public since it belongs to a confidential epic')
+        return _('This issue cannot be made public because it belongs to a confidential epic.')
       end
 
-      _('this issue cannot be assigned to a confidential epic since it is public')
+      _('This issue cannot be assigned to a confidential epic because it is public.')
     end
   end
 end

ee/spec/models/issue_spec.rb

@@ -290,7 +290,7 @@ RSpec.describe Issue do
             issue.epic = epic
 
             expect(issue).not_to be_valid
-            expect(issue.errors.messages[:issue]).to include(/this issue cannot be assigned to a confidential epic since it is public/)
+            expect(issue.errors.messages[:base]).to include(/This issue cannot be assigned to a confidential epic because it is public./)
           end
         end
 
@@ -319,7 +319,7 @@ RSpec.describe Issue do
               issue.confidential = false
 
               expect(issue).not_to be_valid
-              expect(issue.errors.messages[:issue]).to include(/this issue cannot be made public since it belongs to a confidential epic/)
+              expect(issue.errors.messages[:base]).to include(/This issue cannot be made public because it belongs to a confidential epic./)
             end
           end
         end
@@ -339,7 +339,7 @@ RSpec.describe Issue do
             issue.epic = epic
 
             expect(issue).not_to be_valid
-            expect(issue.errors.messages[:issue]).to include(/this issue cannot be assigned to a confidential epic since it is public/)
+            expect(issue.errors.messages[:base]).to include(/This issue cannot be assigned to a confidential epic because it is public./)
           end
         end
       end

locale/gitlab.pot

@@ -36698,6 +36698,12 @@ msgstr ""
 msgid "This is your current session"
 msgstr ""
 
+msgid "This issue cannot be assigned to a confidential epic because it is public."
+msgstr ""
+
+msgid "This issue cannot be made public because it belongs to a confidential epic."
+msgstr ""
+
 msgid "This issue is confidential and should only be visible to team members with at least Reporter access."
 msgstr ""
 
@@ -43531,12 +43537,6 @@ msgstr ""
 msgid "this document"
 msgstr ""
 
-msgid "this issue cannot be assigned to a confidential epic since it is public"
-msgstr ""
-
-msgid "this issue cannot be made public since it belongs to a confidential epic"
-msgstr ""
-
 msgid "time summary"
 msgstr ""