ci(github): add GitHub Actions workflow to update cask formulas

.github/workflows/update-formulas.yml

@@ -0,0 +1,56 @@
+---
+name: Update Formulas
+on:
+  schedule:
+    - cron: "0 3 * * *"
+  workflow_dispatch:
+    inputs:
+      extraArgs:
+        description: "Extra arguments passed to emacs-builder cask update"
+        required: false
+        default: ""
+
+jobs:
+  update:
+    runs-on: macos-10.15
+    steps:
+      - name: Checkout tap repository
+        uses: actions/checkout@v2
+        with:
+          path: tap
+      - name: Symlink homebrew tap
+        run: |
+          mkdir -p '$(brew --repo)/Library/Taps/jimeh'
+          ln -s '${{ github.workspace }}/tap' \
+             '$(brew --repo)/Library/Taps/jimeh/homebrew-emacs-builds'
+      - name: brew livecheck
+        run: >-
+          brew livecheck --json --quiet --tap jimeh/emacs-builds
+          > livecheck-results.json
+      - name: Upload livecheck-results.json artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: livecheck-results.json
+          path: livecheck-results.json
+          if-no-files-found: error
+      - name: Checkout build-emacs-for-macos for emacs-builder tool
+        uses: actions/checkout@v2
+        with:
+          repository: jimeh/build-emacs-for-macos
+          ref: "v0.6.1"
+          path: builder
+      - uses: actions/setup-go@v2
+        with:
+          go-version: 1.16
+      - name: Pre-build emacs-builder tool
+        run: make build
+        working-directory: builder
+      - name: Update Cask formulas
+        run: >-
+          builder/bin/emacs-builder cask update
+          --builds-repository jimeh/emacs-builds
+          --templates-dir tap/templates
+          ${{ github.event.inputs.extraArgs }}
+          livecheck-results.json
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}