Use macOS 12 for test workflows, 11 will soon be deprecated

More info: https://github.blog/changelog/2024-05-20-actions-upcoming-changes-to-github-hosted-macos-runners/

Change-Id: I7dc2a854d2cd19d776db40c5d01016b98760d487

.github/workflows/test.yml

@@ -12,7 +12,7 @@ concurrency:
 
 jobs:
   instrumentation_tests:
-    runs-on: macos-11
+    runs-on: macos-12
     if: github.repository == 'seedvault-app/seedvault'
     timeout-minutes: 80
     strategy: