[#4832] Fixed json schema matcher in Objects API

This change has been made because we are not able to know if the type is
the correct one when no format is defined in the variable. This is left
to the user and we assume that the mapping is valid.

Backport-of: #4938

src/openforms/registrations/contrib/objects_api/json_schema.py

@@ -200,7 +200,7 @@ def json_schema_matches(
     if "string" in target_types and (target_format := target_schema.get("format")):
         variable_format = variable_schema.get("format")
         if variable_format is None:
-            return False
+            return True
         return variable_format == target_format
 
     return True

src/openforms/registrations/contrib/objects_api/tests/test_json_schema.py

@@ -434,7 +434,7 @@ def test_json_schema_matches(self):
             variable_schema = {"type": "string"}
             target_schema = {"type": "string", "format": "email"}
 
-            self.assertFalse(
+            self.assertTrue(
                 json_schema_matches(
                     variable_schema=variable_schema, target_schema=target_schema
                 )