Use macos-10.15 runner

Author: mobecher

.github/workflows/deploy-macOS.yml

@@ -19,7 +19,7 @@ jobs:
   # This workflow contains a single job called "build"
   build:
     # The type of runner that the job will run on
-    runs-on: macos-11
+    runs-on: macos-10.15
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps: