ci: restore CODE_SIGNING_* vars for macOS

These were accidentally deleted when shuffling macOS setup steps to an
`macos-setup/action.yml` and back. These variables make Xcode behavior
consistent across different GHA images.

Author: cwillisf

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

@@ -51,6 +51,8 @@ runs:
       env:
         CONFIG: Debug
         ARTIFACT_TAG: Debug
+        CODE_SIGNING_ALLOWED: ${{ inputs.sign }}
+        CODE_SIGNING_REQUIRED: ${{ inputs.sign }}
       shell: bash
       run: |
         set -x # debug trace