ci: add RubyGems publish workflow triggered on v* tags

Author: nficano

.github/workflows/publish.yml

@@ -0,0 +1,44 @@
+name: publish
+
+on:
+  push:
+    tags:
+      - 'v*'
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Version tag to publish (e.g. v1.0.0)'
+        required: true
+
+permissions:
+  contents: read
+
+jobs:
+  publish:
+    name: Publish to RubyGems
+    runs-on: ubuntu-latest
+    environment: rubygems
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@c4e5b1316158f92e3d49443a9d58b31d25ac0f8f # v1.306.0
+        with:
+          ruby-version: .ruby-version
+          bundler-cache: true
+
+      - name: Build gem
+        run: gem build arcp.gemspec
+
+      - name: Publish to RubyGems
+        env:
+          GEM_HOST_API_KEY: ${{ secrets.RUBYGEMS_API_KEY }}
+        run: |
+          mkdir -p ~/.gem
+          printf -- "---\n:rubygems_api_key: %s\n" "$GEM_HOST_API_KEY" > ~/.gem/credentials
+          chmod 0600 ~/.gem/credentials
+          gem push arcp-*.gem
+          rm -f ~/.gem/credentials