remove g++-9

Author: Stig Rune Sellevag

.github/workflows/cmake.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        compiler: [g++-9, g++-10, g++-11, clang++-12, clang++-13, clang++-14]
+        compiler: [g++-10, g++-11, clang++-12, clang++-13, clang++-14]
 
     steps:
     - uses: actions/checkout@v3