squash: remove source gem matrix from main.yml

it's been reproduced in test-gem.yml

Author: flavorjones

.github/workflows/main.yml

@@ -272,82 +272,6 @@ jobs:
     - name: Run Ruby tests with valgrind
       run: bundle exec rake test:valgrind
 
-  gem-package:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v6
-    - uses: ruby/setup-ruby@v1
-      with:
-        ruby-version: head
-        bundler-cache: true
-    - run: bundle config --local frozen false
-    - run: bundle exec rake build:dev
-    - uses: actions/upload-artifact@v7
-      with:
-        name: gem-package
-        path: pkg
-        retention-days: 1
-
-  gem-install:
-    needs: ["gem-package"]
-    strategy:
-      fail-fast: false
-      matrix:
-        target:
-          - { ruby: "2.7", os: "ubuntu-latest", gemfile: "2.7" }
-          - { ruby: "3.0", os: "ubuntu-latest", gemfile: "3.0" }
-          - { ruby: "3.1", os: "ubuntu-latest", gemfile: "3.1" }
-          - { ruby: "3.2", os: "ubuntu-latest", gemfile: "3.2" }
-          - { ruby: "3.3", os: "ubuntu-latest", gemfile: "3.3" }
-          - { ruby: "3.4", os: "ubuntu-latest", gemfile: "3.4" }
-          - { ruby: "4.0", os: "ubuntu-latest", gemfile: "4.0" }
-          - { ruby: "head", os: "ubuntu-latest", gemfile: "4.1" }
-          - { ruby: "jruby", os: "ubuntu-latest", gemfile: ".." }
-          - { ruby: "truffleruby", os: "ubuntu-latest", gemfile: ".." }
-
-          - { ruby: "2.7", os: "macos-latest", gemfile: "2.7" }
-          - { ruby: "3.0", os: "macos-latest", gemfile: "3.0" }
-          - { ruby: "3.1", os: "macos-latest", gemfile: "3.1" }
-          - { ruby: "3.2", os: "macos-latest", gemfile: "3.2" }
-          - { ruby: "3.3", os: "macos-latest", gemfile: "3.3" }
-          - { ruby: "3.4", os: "macos-latest", gemfile: "3.4" }
-          - { ruby: "4.0", os: "macos-latest", gemfile: "4.0" }
-          - { ruby: "head", os: "macos-latest", gemfile: "4.1" }
-          - { ruby: "jruby", os: "macos-latest", gemfile: ".." }
-          - { ruby: "truffleruby", os: "macos-latest", gemfile: ".." }
-
-          - { ruby: "2.7", os: "windows-latest", gemfile: "2.7" }
-          - { ruby: "3.0", os: "windows-latest", gemfile: "3.0" }
-          - { ruby: "3.1", os: "windows-latest", gemfile: "3.1" }
-          - { ruby: "3.2", os: "windows-latest", gemfile: "3.2" }
-          - { ruby: "3.3", os: "windows-latest", gemfile: "3.3" }
-          - { ruby: "3.4", os: "windows-latest", gemfile: "3.4" }
-          - { ruby: "4.0", os: "windows-latest", gemfile: "4.0" }
-          - { ruby: "head", os: "windows-latest", gemfile: "4.1" }
-          - { ruby: "jruby", os: "windows-latest", gemfile: ".." }
-    env:
-      BUNDLE_GEMFILE: gemfiles/${{ matrix.target.gemfile }}/Gemfile
-    runs-on: ${{ matrix.target.os }}
-    steps:
-    - uses: actions/checkout@v6
-    - uses: ruby/setup-ruby@v1
-      with:
-        ruby-version: ${{ matrix.target.ruby }}
-    - uses: actions/download-artifact@v8
-      with:
-        name: gem-package
-        path: pkg
-    - run: |
-        gem install --local pkg/prism-*.gem
-        gem list -d prism
-      shell: bash
-    - name: Run tests
-      run: |
-        bundle install
-        rm -rf lib ext # ensure we don't use the local files
-        rake test
-      shell: bash
-
   gcc-analyzer:
     runs-on: ubuntu-latest
     steps: