ci: Use Local Execution, Remote Caching (LERC) for fork PRS (#48323)

cleanup

Co-authored-by: trop[bot] <37223003+trop[bot]@users.noreply.github.com>
Co-authored-by: John Kleinschmidt <jkleinsc@electronjs.org>

.github/actions/build-electron/action.yml

@@ -44,6 +44,14 @@ runs:
     - name: Add Clang problem matcher
       shell: bash
       run: echo "::add-matcher::src/electron/.github/problem-matchers/clang.json"
+    - name: Setup Siso for fork pull requests
+      if: ${{ github.event.pull_request.head.repo.full_name != github.repository }}
+      shell: bash
+      run: |
+        # Use Local Execution, Remote Caching (LERC). Checks the remote cache for action
+        # matches and uses existing results if a match is found. If not, execution of the
+        # action is performed locally.
+        echo "RBE_exec_strategy=local" >> $GITHUB_ENV
     - name: Build Electron ${{ inputs.step-suffix }}
       shell: bash
       run: |