deprecate_old_osx (#383)

Author: gijzelaerr

.github/workflows/osx.yml

@@ -6,7 +6,7 @@ on:
     branches: [ master ]
 jobs:
   osx_wheel:
-    runs-on: macos-10.15
+    runs-on: macos-11
     steps:
       - name: Checkout
         uses: actions/checkout@v2