Update macOS version in GitHub workflows to macos-12

.github/workflows/ci.yml

@@ -202,7 +202,7 @@ jobs:
 # We no longer run the macos tests, to make CI faster.
 # macos:
 
-#   runs-on: macos-11
+#   runs-on: macos-12
 #   strategy:
 #     fail-fast: true
 #     matrix:

.github/workflows/nightly.yml

@@ -69,7 +69,7 @@ jobs:
 
   macos:
 
-    runs-on: macos-11
+    runs-on: macos-12
 
     steps:
     - uses: actions/checkout@v4

.github/workflows/release-candidate.yml

@@ -77,7 +77,7 @@ jobs:
 
   macos:
 
-    runs-on: macos-11
+    runs-on: macos-12
 
     steps:
     - uses: actions/checkout@v4