Move GCC builders to clang 17, as the 18 package is missing libclang

Author: danakj

.github/workflows/ci.yml

@@ -75,7 +75,7 @@ jobs:
             build_type: "Release",
             cc: "gcc-13",
             cxx: "g++-13",
-            clang_version: 18,
+            clang_version: 17,
             installed_clang_version: 14
           }
 

.github/workflows/try.yml

@@ -78,7 +78,7 @@ jobs:
             build_type: "Release",
             cc: "gcc-13",
             cxx: "g++-13",
-            clang_version: 18,
+            clang_version: 17,
             installed_clang_version: 14
           }