Include the service name in the error message when it's extends does not exist

Signed-off-by: Jan Matějka <jan@matejka.ninja>

Author: jan-matejka

podman_compose.py

@@ -1942,7 +1942,12 @@ def resolve_extends(
             normalize_service(from_service, subdirectory)
         else:
             from_service = services.get(from_service_name, {}).copy()
-            del from_service["_deps"]
+            try:
+                del from_service["_deps"]
+            except KeyError:
+                raise KeyError(
+                    f"{from_service_name} not found at services.{name}.extends definition"
+                )
             try:
                 del from_service["extends"]
             except KeyError: