python: Fix PythonBuildConfig.get()

Author: mgorny

mesonbuild/dependencies/python.py

@@ -113,7 +113,7 @@ def __contains__(self, key: str) -> bool:
 
     def get(self, key: str, default: T.Any = None) -> T.Any:
         try:
-            self[key]
+            return self[key]
         except KeyError:
             return default