Added macos-12 and 13 testing in addition to latest (which is 14).

Author: Lastique

.github/workflows/ci.yml

@@ -283,8 +283,14 @@ jobs:
               - libc++abi-15-dev
 
           - toolset: clang
-            cxxstd: "11,14,17,2a"
-            os: macos-latest
+            cxxstd: "11,14,17,20,2b"
+            os: macos-12
+          - toolset: clang
+            cxxstd: "11,14,17,20,2b"
+            os: macos-13
+          - toolset: clang
+            cxxstd: "11,14,17,20,2b"
+            os: macos-14
 
           - name: CMake tests
             cmake_tests: 1