mesh-2092: fix mypy issues

Author: james-bradley-nhs

nhs_aws_helpers/async_s3_object_reader.py

@@ -123,7 +123,7 @@ async def read(self, num: Optional[int] = None) -> Union[str, bytes]:
         body = await self._maybe_get_body()
 
         if num is None:
-            chunk = body.read()
+            chunk = cast(Union[str, bytes], body.read())
             if self._encoding:
                 chunk = self.ensure_valid_chunk(chunk)
             else:

nhs_aws_helpers/s3_object_reader.py

@@ -129,7 +129,7 @@ def read(self, num: Optional[int] = None) -> Union[str, bytes]:
             return chunk
 
         if num is None:
-            chunk = self.body.read()
+            chunk = cast(Union[str, bytes], self.body.read())
             if self._encoding:
                 chunk = self.ensure_valid_chunk(chunk)
             else: