Revert unintended change to azure-keyvault-keys KeyProperties.tags type annotation

Author: singhalrohit4u

sdk/keyvault/azure-keyvault-keys/azure/keyvault/keys/_models.py

@@ -252,11 +252,11 @@ def recovery_level(self) -> Optional[str]:
         return self._attributes.recovery_level if self._attributes else None
 
     @property
-    def tags(self) -> Dict[str, str]:
+    def tags(self) -> Optional[Dict[str, str]]:
         """Application specific metadata in the form of key-value pairs.
 
         :returns: A dictionary of tags attached to the key.
-        :rtype: dict[str, str]
+        :rtype: dict[str, str] or None
         """
         return self._tags