Continuous Integration: Add macos-15 OS explicitly, to check for build problems

Author: davidfstr

.github/workflows/main.yml

@@ -5,7 +5,7 @@ jobs:
   test:
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-latest, macos-latest, macos-15, windows-latest]
         ruby-version: ['4.0', '3.4', '3.3', '3.2', '3.1', '3.0', '2.7', truffleruby]
         # conformance require perl because of that we 
         # only run unit tests on windows