Tools: Add build workflow to create build automatically

.github/workflows/build.yml

@@ -0,0 +1,49 @@
+name: Build files and push to `build` branch.
+
+on:
+    push:
+        branches:
+            - trunk
+        paths:
+            - themes/**
+            - plugins/**
+    # Enable manually running action if necessary.
+    workflow_dispatch:
+
+jobs:
+    build:
+        runs-on: ubuntu-latest
+        steps:
+            - name: Checkout repository
+              uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+
+            - name: Setup
+              uses: WordPress/wporg-repo-tools/.github/actions/setup@trunk
+              with:
+                token: ${{ secrets.GITHUB_TOKEN }}
+
+            - name: Remove build artifacts
+              run: |
+                  rm -rf themes/wporg-5ftf/node_modules themes/wporg-5ftf-2024/node_modules plugins/wporg-5ftf/node_modules
+
+            - name: Ignore .gitignore
+              run: |
+                  git add themes/wporg-5ftf/* --force
+                  git add themes/wporg-5ftf/* --force
+                  git add plugins/wporg-5ftf/* --force
+
+            - name: Append build number to version
+              run: |
+                current_version=$(grep -oP 'Version: \K[0-9]+\.[0-9]+\.[0-9]+' themes/wporg-5ftf-2024/style.css)
+                new_version="${current_version}-${GITHUB_SHA::7}"
+                sed -i "s/Version: $current_version/Version: $new_version/" themes/wporg-5ftf-2024/style.css
+                sed -i "s/\"version\": \"0.1.0\"/\"version\": \"$new_version\"/" themes/wporg-5ftf-2024/build/**/block.json
+                
+            - name: Commit and push
+              # Using a specific hash here instead of a tagged version, for risk mitigation, since this action modifies our repo.
+              uses: actions-js/push@a52398fac807b0c1e5f1492c969b477c8560a0ba # 1.3
+              with:
+                  github_token: ${{ secrets.GITHUB_TOKEN }}
+                  branch: build
+                  force: true
+                  message: 'Build: ${{ github.sha }}'