fix(cdk-diff): REVERT github now requires metadata grant [INFRA-52676] (#340)

This reverts commit 2699a27.

Alas, I trusted GitHub CoPilot and it hallucinated.

Author: ahammond

src/cdk-diff-workflow.ts

@@ -28,7 +28,6 @@ export module cdkDiffWorkflow {
       permissions: {
         'id-token': 'write',
         contents: 'write',
-        metadata: 'write',
         'pull-requests': 'write',
       },
       jobs: {