Tweak bundler installation

Author: etagwerker

.github/workflows/test.yml

@@ -4,10 +4,10 @@ name: Test
 on:
   push:
     branches:
-    - main
+      - main
   pull_request:
     branches:
-    - main
+      - main
 jobs:
   test:
     runs-on: ubuntu-latest
@@ -22,12 +22,18 @@ jobs:
         with:
           ruby-version: ${{ matrix.ruby-version }}
           bundler-cache: true
+      - name: Install Bundler
+        run: |
+          if [[ "${{ matrix.ruby-version }}" == "2.6" || "${{ matrix.ruby-version }}" == "2.7" ]]; then
+            gem install bundler -v "~> 2.4.0"
+          else
+            gem install bundler
+          fi
       - name: Build and run tests
         env:
           COVERAGE: true
           TERM: xterm
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
         run: |
-          gem install bundler
           bundle install --jobs 4 --retry 3
-          bundle exec rake test
+          bundle exec rake test