Create gem-push.yml

Adds GitHub action for publishing new versions (GitHub releases) to RubyGems.

.github/workflows/gem-push.yml

@@ -0,0 +1,33 @@
+name: Ruby Gem
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build:
+    name: Build + Publish
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '3.2'
+        bundler-cache: true
+
+    - name: Publish to RubyGems
+      run: |
+        mkdir -p $HOME/.gem
+        touch $HOME/.gem/credentials
+        chmod 0600 $HOME/.gem/credentials
+        printf -- "---\n:rubygems_api_key: ${GEM_HOST_API_KEY}\n" > $HOME/.gem/credentials
+        gem build *.gemspec
+        gem push *.gem
+      env:
+        GEM_HOST_API_KEY: "${{secrets.RUBYGEMS_AUTH_TOKEN}}"