Fix not all events being shown in group dashboard

The group activity feed was limited to the first 20 projects found
in the group, which caused activity from some projects to be omitted.
A limit of 20 is applied to the query for events, so the
extra pagination does little in the way of performance.

Closes #42560

app/controllers/groups_controller.rb

@@ -150,7 +150,6 @@ class GroupsController < Groups::ApplicationController
     @projects = GroupProjectsFinder.new(params: params, group: group, options: options, current_user: current_user)
                   .execute
                   .includes(:namespace)
-                  .page(params[:page])
 
     @events = EventCollection
       .new(@projects, offset: params[:offset].to_i, filter: event_filter)

changelogs/unreleased/sh-fix-events-collection.yml

+---
+title: Fix not all events being shown in group dashboard
+merge_request:
+author:
+type: fixed

spec/controllers/groups_controller_spec.rb

@@ -85,6 +85,30 @@ describe GroupsController do
     end
   end
 
+  describe 'GET #activity' do
+    render_views
+
+    before do
+      sign_in(user)
+      project
+    end
+
+    context 'as json' do
+      it 'includes all projects in event feed' do
+        3.times do
+          project = create(:project, group: group)
+          create(:event, project: project)
+        end
+
+        get :activity, id: group.to_param, format: :json
+
+        expect(response).to have_gitlab_http_status(200)
+        expect(json_response['count']).to eq(3)
+        expect(assigns(:projects).limit_value).to be_nil
+      end
+    end
+  end
+
   describe 'POST #create' do
     context 'when creating subgroups', :nested_groups do
       [true, false].each do |can_create_group_status|