ci(gem): add rubygems build-push job

.github/workflows/gem-push.yml

@@ -0,0 +1,30 @@
+name: Ruby Gem
+
+on:
+  push:
+    tags: [ v* ]
+
+jobs:
+  build:
+    name: Build + Publish
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby 2.6
+      uses: actions/setup-ruby@v1
+      with:
+        ruby-version: 2.6.x
+    - 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}}"