only use gem source for linter tests - to fix https://www.redmine.org/issues/35028 - next try

.github/workflows/linters.yml

@@ -12,6 +12,10 @@ jobs:
     steps:
     - uses: actions/checkout@v1
 
+    - name: Set Gemfile
+      run: |
+        cp test/support/gemfile.rb Gemfile
+
     - name: Setup Ruby
       uses: ruby/setup-ruby@v1
       with:
@@ -20,7 +24,6 @@ jobs:
 
     - name: Setup gems
       run: |
-        cp test/support/gemfile.rb Gemfile
         bundle install --jobs 4 --retry 3
 
     - name: Run RuboCop

.github/workflows/tests.yml

@@ -86,8 +86,6 @@ jobs:
       - name: Prepare Redmine source
         working-directory: redmine
         run: |
-          sed -i '/rubocop/d' Gemfile
-          rm -f .rubocop*
           cp plugins/additionals/test/support/database-${{ matrix.db }}.yml config/database.yml
           cp plugins/additionals/test/support/configuration.yml config/configuration.yml