Build/Test Tools: Test certificate-related scripts in 6.8 branch.

This makes use of the new input added in [60765], which runs the `copy:certificates` and `build:certificates` Grunt tasks to ensure there are no uncommitted changes to files under version control.

Follow up to [60765].

See #63939.

git-svn-id: https://develop.svn.wordpress.org/branches/6.8@60766 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

.github/workflows/test-build-processes.yml

@@ -63,10 +63,14 @@ jobs:
             directory: 'build'
             save-build: true
             prepare-playground: ${{ github.event_name == 'pull_request' && true || '' }}
+          # Test certificate build commands with Linux only.
+          - os: ubuntu-24.04
+            test-certificates: true
 
     with:
       os: ${{ matrix.os }}
       directory: ${{ matrix.directory }}
+      test-certificates: ${{ matrix.test-certificates && true || false }}
       save-build: ${{ matrix.save-build && matrix.save-build || false }}
       prepare-playground: ${{ matrix.prepare-playground && matrix.prepare-playground || false }}