pin macos test runners to macos-12 (#1016) (#1020)

(cherry picked from commit c5742f2)

Author: mikealfare

.github/workflows/main.yml

@@ -174,7 +174,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest, macos-12, windows-latest]
         python-version: ["3.7", "3.8", "3.9", "3.10"]
 
     steps: