ci: reapply patches if PR base branch updates them (#49516)

.github/workflows/build.yml

@@ -57,6 +57,7 @@ jobs:
         src: ${{ steps.filter.outputs.src }}
         build-image-sha: ${{ steps.set-output.outputs.build-image-sha }}
         docs-only: ${{ steps.set-output.outputs.docs-only }}
+        has-patches: ${{ steps.filter.outputs.patches }}
     steps:
     - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8
       with:
@@ -73,6 +74,9 @@ jobs:
             - CODE_OF_CONDUCT.md
           src:
             - '!docs/**'
+          patches:
+            - DEPS
+            - 'patches/**'
     - name: Set Outputs for Build Image SHA & Docs Only
       id: set-output
       run: |
@@ -105,6 +109,41 @@ jobs:
       container: '{"image":"ghcr.io/electron/build:${{ needs.checkout-linux.outputs.build-image-sha }}","options":"--user root","volumes":["/mnt/cross-instance-cache:/mnt/cross-instance-cache"]}'
     secrets: inherit
 
+  # Apply Patches Job
+  apply-patches:
+    needs: setup
+    if: ${{ needs.setup.outputs.has-patches == 'true' }}
+    runs-on: electron-arc-centralus-linux-amd64-32core
+    permissions:
+      contents: read
+    container:
+      image: ghcr.io/electron/build:${{ needs.setup.outputs.build-image-sha }}
+      options: --user root
+      volumes:
+        - /mnt/cross-instance-cache:/mnt/cross-instance-cache
+        - /var/run/sas:/var/run/sas
+    env:
+      CHROMIUM_GIT_COOKIE: ${{ secrets.CHROMIUM_GIT_COOKIE }}
+      GCLIENT_EXTRA_ARGS: '--custom-var=checkout_arm=True --custom-var=checkout_arm64=True'
+    steps:
+    - name: Checkout Electron
+      uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8
+      with:
+        path: src/electron
+        fetch-depth: 0
+        ref: ${{ github.event.pull_request.head.sha }}
+    - name: Rebase onto Base Branch
+      working-directory: src/electron
+      run: |
+        git config user.email "electron@github.com"
+        git config user.name "Electron Bot"
+        git fetch origin ${{ github.event.pull_request.base.ref }}
+        git rebase origin/${{ github.event.pull_request.base.ref }}
+    - name: Checkout & Sync & Save
+      uses: ./src/electron/.github/actions/checkout
+      with:
+        target-platform: linux
+
   # Checkout Jobs
   checkout-macos:
     needs: setup