Workflow to update zonetab

.github/workflows/update.yml

@@ -0,0 +1,36 @@
+name: update
+
+on:
+  push:
+  schedule:
+    - cron: '0 10 * * 3'
+
+jobs:
+  update:
+    name: update zonetab
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      run: sudo apt-get --no-install-recommends -q -y install ruby-dev gperf
+    - name: Install dependencies
+      run: sudo gem install --no-document nokogiri
+    - name: Update zonetab
+      working-directory: ext/date
+      run: |
+        make -f prereq.mk update-zonetab
+        make -f prereq.mk zonetab.h
+      env:
+        top_srcdir: ../..
+        srcdir: .
+        RUBY: /usr/bin/ruby
+    - name: Check diffs
+      run: |
+        git config --global user.email "nobu@ruby-lang.org"
+        git config --global user.name "Nobuyoshi Nakada"
+        git commit --allow-empty --message="Update zonetab.h at $(date +%F)" ext/date
+        git diff --no-ext-diff --ignore-submodules --exit-code HEAD^..HEAD ||
+        {
+          git pull --ff-only origin ${GITHUB_REF#refs/heads/}
+          git push origin ${GITHUB_REF#refs/heads/}
+        }