Fix Bugs with oci/layer.py (#166)

* Fix bug with __iter__() not returning Iterator
* Fix bug with __delitem__() always raising KeyError
* Fix bug with __setitem__() alwasy raising KeyError

Author: ByteOtter

src/gardenlinux/oci/layer.py

@@ -91,10 +91,10 @@ def __getitem__(self, key):
 
         if key == "annotations":
             return self._annotations
-
-        raise KeyError(
-            f"'{self.__class__.__name__}' object is not subscriptable except for keys: {_SUPPORTED_MAPPING_KEYS}"
-        )
+        else:
+            raise KeyError(
+                f"'{self.__class__.__name__}' object is not subscriptable except for keys: {_SUPPORTED_MAPPING_KEYS}"
+            )
 
     def __iter__(self):
         """
@@ -104,7 +104,7 @@ def __iter__(self):
         :since:  0.7.0
         """
 
-        iter(_SUPPORTED_MAPPING_KEYS)
+        return iter(_SUPPORTED_MAPPING_KEYS)
 
     def __len__(self):
         """
@@ -128,10 +128,10 @@ def __setitem__(self, key, value):
 
         if key == "annotations":
             self._annotations = value
-
-        raise KeyError(
-            f"'{self.__class__.__name__}' object is not subscriptable except for keys: {_SUPPORTED_MAPPING_KEYS}"
-        )
+        else:
+            raise KeyError(
+                f"'{self.__class__.__name__}' object is not subscriptable except for keys: {_SUPPORTED_MAPPING_KEYS}"
+            )
 
     @staticmethod
     def generate_metadata_from_file_name(file_name: PathLike | str, arch: str) -> dict: