macOS-11 runner not public yet.

Author: cboulay

.github/workflows/cppcmake.yml

@@ -43,11 +43,8 @@ jobs:
           arch: "i386"
           qt_arch: "win32_msvc2019"
           qt_ver: "5.15.2"
-        - name: "macOS-latest"
-          os: "macos-latest"
-          qt_ver: "6.1.0"
-        - name: "macOS-11"
-          os: "macos-11"
+        - name: "macOS-10"
+          os: "macos-10.15"
           qt_ver: "6.1.0"
     steps:
     - uses: actions/checkout@v2