Fix exception thrown when attempting to notify appservice sender

Fix #11025

Before in [`user_directory_handler._handle_deltas`, we just checked for `is_support_user(user_id)`](https://github.com/matrix-org/synapse/pull/10960/files#diff-e02a9a371e03b8615b53c6b6552f76fc7d3ef58931ca64d28b3512caf305449fL232) which works just fine.
Now with #10960, we [call `should_include_local_user_in_dir`](https://github.com/matrix-org/synapse/pull/10960/files#diff-e02a9a371e03b8615b53c6b6552f76fc7d3ef58931ca64d28b3512caf305449fR229) which does a [bunch of additional checks](https://github.com/matrix-org/synapse/blob/e79ee48313404abf8fbb7c88361e4ab1efa29a81/synapse/storage/databases/main/user_directory.py#L382-L398) which aren't all compatible with the main appservice sender (main bridge user/sender). More specifically, we can't check the `users` database table for whether the user is deactivated.

In the `should_include_local_user_in_dir` checks, we should return early if we encounter a main appservice sender before the incompatible checks.

synapse/storage/databases/main/user_directory.py

@@ -383,6 +383,10 @@ async def should_include_local_user_in_dir(self, user: str) -> bool:
         """Certain classes of local user are omitted from the user directory.
         Is this user one of them?
         """
+        # The main app service sender isn't usually contactable, so exclude them
+        if self.get_app_service_by_user_id(user) is not None:
+            return False
+
         # App service users aren't usually contactable, so exclude them.
         if self.get_if_app_services_interested_in_user(user):
             # TODO we might want to make this configurable for each app service

tests/handlers/test_user_directory.py

@@ -295,6 +295,27 @@ def test_handle_local_profile_change_with_appservice_user(self) -> None:
         profile = self.get_success(self.store.get_user_in_directory(as_user_id))
         self.assertTrue(profile is None)
 
+    def test_handle_local_profile_change_with_appservice_sender(self) -> None:
+        # profile is not in directory
+        profile = self.get_success(
+            self.store.get_user_in_directory(self.appservice.sender)
+        )
+        self.assertTrue(profile is None)
+
+        # update profile
+        profile_info = ProfileInfo(avatar_url="avatar_url", display_name="4L1c3")
+        self.get_success(
+            self.handler.handle_local_profile_change(
+                self.appservice.sender, profile_info
+            )
+        )
+
+        # profile is still not in directory
+        profile = self.get_success(
+            self.store.get_user_in_directory(self.appservice.sender)
+        )
+        self.assertTrue(profile is None)
+
     def test_handle_user_deactivated_support_user(self) -> None:
         s_user_id = "@support:test"
         self.get_success(

tests/storage/test_user_directory.py

@@ -364,6 +364,21 @@ def test_population_excludes_appservice_user(self) -> None:
         # Check the AS user is not in the directory.
         self._check_room_sharing_tables(user, public, private)
 
+    def test_population_excludes_appservice_sender(self) -> None:
+        user = self.register_user("user", "pass")
+        token = self.login(user, "pass")
+
+        # Join the AS sender to rooms owned by the normal user.
+        public, private = self._create_rooms_and_inject_memberships(
+            user, token, self.appservice.sender
+        )
+
+        # Rebuild the directory.
+        self._purge_and_rebuild_user_dir()
+
+        # Check the AS sender is not in the directory.
+        self._check_room_sharing_tables(user, public, private)
+
     def test_population_conceals_private_nickname(self) -> None:
         # Make a private room, and set a nickname within
         user = self.register_user("aaaa", "pass")