Fix macos build (#3)

Author: unterumarmung

.github/workflows/macos.yml

@@ -10,7 +10,6 @@ jobs:
       matrix:
         config:
         - { os: macos-10.15, xcode: "12.0.1" } # https://github.com/actions/virtual-environments/blob/main/images/macos/macos-10.15-Readme.md#xcode
-        - { os: macos-11.0, xcode: "11.7" }    # https://github.com/actions/virtual-environments/blob/main/images/macos/macos-11.0-Readme.md#xcode
         build: [Debug, Release]
 
     name: "xcode${{matrix.config.xcode}}:${{matrix.build}}"