Simplify my life by removing paranoia tests

Commonmarker currently has three different test suites related to the
gem build:

1. The compilation output is tested
2. The gem can be installed on another platform
3. A generic version of the gem can be installed on a platform with
sufficient Ruby/Rust tooling

Of these, only the first is the most relevant. #2 suggests an error in
the build pipeline, and #3 opens the door to supporting platforms that
are uncommon. In order to minimize support work
on my end, I'm going to nix the last two tests; as
well, I can abstract the first test into a GitHub Action for other
oxidizers to use.

.github/workflows/cruby-build-and-install.yml

@@ -47,102 +47,7 @@ jobs:
           platform: ${{ matrix.platform }}
           ruby-versions: "3.1,3.2" # SUPPORTED_RUBY_VERSIONS
 
-      - name: "Test gem build"
-        run: |
-          ./script/test-gem-build gems ${{matrix.platform}}
-
-      - uses: actions/upload-artifact@v3
-        with:
-          name: "${{ env.CACHE_KEY_PREFIX }}-${{matrix.platform}}-gem"
-          path: ${{ steps.cross-gem.outputs.gem-path }}
-          retention-days: 1
-
-  cruby-x86_64-linux-install:
-     needs: ["cruby-package"]
-     strategy:
-       fail-fast: false
-       matrix:
-         ruby: ["3.1", "3.2"] # SUPPORTED_RUBY_MATRIX
-     runs-on: ubuntu-latest
-     steps:
-       - uses: actions/checkout@v3
-
-       - uses: ruby/setup-ruby@v1
-         with:
-           rubygems: latest
-           ruby-version: "${{matrix.ruby}}"
-
-       - uses: actions/download-artifact@v3
-         with:
-           name: ${{ env.CACHE_KEY_PREFIX }}-x86_64-linux-gem
-           path: gems
-       - run: ./script/test-gem-install gems
-
-  cruby-aarch64-linux-install:
-    needs: ["cruby-package"]
-    strategy:
-      fail-fast: false
-      matrix:
-        ruby: ["3.1", "3.2"] # SUPPORTED_RUBY_MATRIX
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v3
-
-      - uses: ruby/setup-ruby@v1
+      - uses: oxidize-rb/actions/cross-gem@add-test-scripts
         with:
-          rubygems: latest
-          ruby-version: "${{matrix.ruby}}"
-
-      - uses: actions/download-artifact@v3
-        with:
-          name: ${{ env.CACHE_KEY_PREFIX }}-aarch64-linux-gem
-          path: gems
-
-      - run: ./script/test-gem-install gems
-
-  cruby-x86_64-darwin-install:
-     needs: ["cruby-package"]
-     strategy:
-       fail-fast: false
-       matrix:
-         ruby: ["3.1", "3.2"] # SUPPORTED_RUBY_MATRIX
-     runs-on: macos-latest
-     steps:
-       - uses: actions/checkout@v3
-
-       - uses: ruby/setup-ruby@v1
-         with:
-           rubygems: latest
-           ruby-version: "${{matrix.ruby}}"
-
-       - uses: actions/download-artifact@v3
-         with:
-           name: ${{ env.CACHE_KEY_PREFIX }}-x86_64-darwin-gem
-           path: gems
-
-       - run: ./script/test-gem-install gems
-
-  # FIXME: does not seem to work
-  # cruby-x64-mingw-ucrt-install:
-  #   needs: ["cruby-package"]
-  #   strategy:
-  #     fail-fast: false
-  #     matrix:
-  #       ruby: ["3.1"]
-  #   runs-on: windows-latest
-  #   steps:
-  #     - uses: ruby/setup-ruby@v1
-
-  #       with:
-  #         ruby-version: "${{matrix.ruby}}"
-
-  #     - uses: actions/download-artifact@v3
-  #       with:
-  #         name: cruby-x64-mingw-ucrt-gem
-  #         path: gems
-
-  #     - run: |
-  #         gem update --system 3.3.22 --no-document
-  #         gem install --verbose --no-document gems/*.gem
-  #         gem list -d commonmarker
-  #         bundle exec ruby -e 'require "commonmarker"; puts Commonmarker.to_html("Hello, _world_")'
+          platform: ${{ matrix.platform }}
+          ruby-versions: "3.1,3.2" # SUPPORTED_RUBY_VERSIONS