Update black, and run auto formatting over the codebase (#9381)

- Update black version to the latest
 - Run black auto formatting over the codebase
    - Run autoformatting according to [`docs/code_style.md
`](80d6dc9783/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

synapse/storage/background_updates.py

@@ -77,7 +77,7 @@ class BackgroundUpdatePerformance:
 
 
 class BackgroundUpdater:
-    """ Background updates are updates to the database that run in the
+    """Background updates are updates to the database that run in the
     background. Each update processes a batch of data at once. We attempt to
     limit the impact of each update by monitoring how long each batch takes to
     process and autotuning the batch size.
@@ -158,8 +158,7 @@ class BackgroundUpdater:
         return False
 
     async def has_completed_background_update(self, update_name: str) -> bool:
-        """Check if the given background update has finished running.
-        """
+        """Check if the given background update has finished running."""
         if self._all_done:
             return True
 
@@ -198,7 +197,8 @@ class BackgroundUpdater:
 
         if not self._current_background_update:
             all_pending_updates = await self.db_pool.runInteraction(
-                "background_updates", get_background_updates_txn,
+                "background_updates",
+                get_background_updates_txn,
             )
             if not all_pending_updates:
                 # no work left to do