Try to fix test suite in GitHub Actions CI for Ruby 2.6

Author: etagwerker

.github/workflows/test.yml

@@ -16,15 +16,12 @@ jobs:
         ruby-version: ["2.5", "2.6", "2.7", "3.0", "3.1", "3.2", "3.3", "3.4"]
 
     steps:
-      - uses: actions/checkout@v1
+      - uses: actions/checkout@v4
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby-version }}
           bundler-cache: true
-      - name: Uninstall existing Bundler
-        run: |
-          gem uninstall bundler -a -x || true
       - name: Install Bundler
         run: |
           if [[ "${{ matrix.ruby-version }}" == "2.5" ]]; then