Acceptance tests: update MacOS runner

The `macos-13` GitHub action runner is being retired; this updates the
runner to the most recent version that runs on Intel.

Updating the MacOS runner to ARM currently breaks. It is covered by PR
#91 — Acceptance tests: Switch macOS runner to ARM.

Author: danielparks

.github/workflows/pr-checks.yaml

@@ -59,7 +59,7 @@ jobs:
             puppet: 7
           - os: ubuntu-latest
             puppet: 8
-          - os: macos-13
+          - os: macos-15-intel
             puppet: 8
     runs-on: ${{ matrix.os }}
 

.sync.yml

@@ -8,4 +8,4 @@
 ---
 .github/workflows/pr-checks.yaml:
   additional-platforms:
-    - macos-13
+    - macos-15-intel