Run CI with macOS-11 to fix issues. This is a temporary fix before the release (#1407)

Signed-off-by: Jean-Christophe Morin <[email protected]>

Author: JeanChristopheMorinPerso

.github/workflows/mac.yaml

@@ -21,7 +21,7 @@ jobs:
     strategy:
       matrix:
         os-version:
-          - 'latest'
+          - '11'
         python-version:
           - '2.7'
           - '3.7'