Adding clang 21 to test matrix

Author: gershnik

.github/workflows/test.yml

@@ -52,7 +52,8 @@ jobs:
             17: 'ubuntu-latest', 
             18: 'ubuntu-latest', 
             19: 'ubuntu-latest', 
-            20: 'ubuntu-latest'
+            20: 'ubuntu-latest',
+            21: 'ubuntu-latest'
           }
           
           hosts = []