Tests: Update mypy error message (#798)

Fixes CI failures. I assume it's because of some changes in django-stubs.

Author: intgr

tests/typecheck/test_exceptions.yml

@@ -46,5 +46,5 @@
     APIException()
     APIException(None, None)
     APIException(1)  # E: Argument 1 to "APIException" has incompatible type "int"; expected "_APIExceptionInput"
-    APIException({'a': 1})  # E: Argument 1 to "APIException" has incompatible type "dict[str, int]"; expected "_APIExceptionInput"
-    APIException({'a': ['test', 1]})  # E: Argument 1 to "APIException" has incompatible type "dict[str, list[str | int]]"; expected "_APIExceptionInput"
+    APIException({'a': 1})  # E: Dict entry 0 has incompatible type "str": "int"; expected "str": "_StrPromise | Sequence[_APIExceptionInput] | Mapping[str, _APIExceptionInput] | None"
+    APIException({'a': ['test', 1]})  # E: List item 1 has incompatible type "int"; expected "_StrPromise | Sequence[_APIExceptionInput] | Mapping[str, _APIExceptionInput] | None"