tests: switch to macOS 11 in os matrix

actions/runner-images#5583

Author: shcheklein

.github/workflows/test.yml

@@ -23,7 +23,7 @@ jobs:
       fail-fast: false
       max-parallel: 3
       matrix:
-        os: [ubuntu-18.04, macos-10.15, windows-2019]
+        os: [ubuntu-18.04, macos-11, windows-2019]
         pyv: ["3.7", "3.8", "3.9", "3.10"]
 
     steps: