gem CI workflow: Check if the gem builds

[bastelfreak]

Use Case

It makes sense to check if a gem still builds within a PR. That ensures that an upcoming release isn't broken. At Vox Pupuli we use the following matrix:

jobs:
  rubocop:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install Ruby ${{ matrix.ruby }}
        uses: ruby/setup-ruby@v1
        with:
          ruby-version: "3.3"
          bundler-cache: true
      - name: Run Rubocop
        run: bundle exec rake rubocop
  test:
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        ruby:
          - "2.7"
          - "3.0"
          - "3.1"
          - "3.2"
          - "3.3"
    name: Ruby ${{ matrix.ruby }}
    steps:
      - uses: actions/checkout@v4
      - name: Install Ruby ${{ matrix.ruby }}
        uses: ruby/setup-ruby@v1
        with:
          ruby-version: ${{ matrix.ruby }}
          bundler-cache: true
      - name: Run tests
        run: bundle exec rake
      - name: Verify gem builds
        run: gem build --strict --verbose *.gemspec

Describe the Solution You Would Like

Run gem builds with gem build --strict --verbose *.gemspec during each PR. The same should be applied for releasing a gem.

Describe Alternatives You've Considered

A clear and concise description of any alternative solutions or features you've considered.

Additional Context

This can be considered as a breaking change for gems without proper dependency boundaries. In those cases the command will fail with --strict. This change shouldn't be implemented in the main branch but rather in something like a v2. See #89

[jordanbreen28]

thanks @bastelfreak! We agree this is a good change to have, and will help catch broken gem builds before they are merged. We have added this to the backlog.