fix: mdstore: fix MetadataStore.dumps(format="md")

MetadataStore.dumps(format="md") was failing with

    TypeError: Object of type dict_items is not JSON serializable

... because self.items() returns dictitems() - while only a dict would be serializable into JSON.

Convert the dictitems back into a dict.

Author: vladimir-mencl-eresearch

src/saml2/mdstore.py

@@ -1693,4 +1693,5 @@ def dumps(self, format="local"):
 
             return "%s" % res
         elif format == "md":
-            return json.dumps(self.items(), indent=2)
+            # self.items() returns dictitems(), convert that back into a dict
+            return json.dumps(dict(self.items()), indent=2)