ci(cmake-multi-platform): use macos-15 to have Clang/LLVM 18

actions/runner-images#10686
actions/runner-images#11486

Author: andreaswachowski

.github/workflows/cmake-multi-platform.yml

@@ -23,7 +23,7 @@ jobs:
       #
       # To add more build types (Release, Debug, RelWithDebInfo, etc.) customize the build_type list.
       matrix:
-        os: [ubuntu-latest, macos-latest]
+        os: [ubuntu-latest, macos-15]
         build_type: [Release]
         c_compiler: [gcc, clang]
         include:
@@ -33,11 +33,11 @@ jobs:
           - os: ubuntu-latest
             c_compiler: clang
             cpp_compiler: clang++
-          - os: macos-latest
+          - os: macos-15
             c_compiler: clang
             cpp_compiler: clang++
         exclude:
-          - os: macos-latest
+          - os: macos-15
             c_compiler: gcc
 
     steps: