ci: replace macos-11 with macos-12 (#618)

Author: xJonathanLEI

.github/workflows/test.yaml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-11]
+        os: [ubuntu-latest, macos-12]
         toolchain: [stable, nightly]
 
     steps: