Alter build-release GH-A workflow to work with the new set of compilers [skip ci]

Author: saxbophone

.github/workflows/build-release.yml

@@ -18,7 +18,7 @@ jobs:
             os: ubuntu-20.04
             cxx: g++-10
           - platform_name: macos
-            os: macos-10.15
+            os: macos-12
             cxx: clang++
           # NOTE: CXX seems to be ignored on Windows, but specify it anyway for consistency
           - platform_name: windows