Specific version of macOS.

.github/workflows/ci.yml

@@ -53,9 +53,9 @@ jobs:
           - "3.11"
         include:
           # On macOS don't bother with 3.8, just to get faster builds.
-          - os: macos-latest
+          - os: macos-12
             python-version: "3.9"
-          - os: macos-latest
+          - os: macos-12
             python-version: "3.11"
           # We only support PyPy on Linux at the moment.
           - os: ubuntu-latest
@@ -165,7 +165,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: macos-latest
+          - os: macos-12
             python-version: "3.9"
             force-foolscap: false
           - os: windows-latest
@@ -248,7 +248,7 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-latest
+          - macos-12
           - windows-latest
           - ubuntu-latest
         python-version: