Pre-emptively fix synapse.storage.types.Connection for future mypy release (#8577)

Fix the Connection protocol according to typeshed's assertions about sqlite3.Connection

changelog.d/8577.misc

+Adjust a protocol-type definition to fit `sqlite3` assertions.
\ No newline at end of file

synapse/storage/database.py

@@ -160,7 +160,7 @@ class LoggingDatabaseConnection:
         self.conn.__enter__()
         return self
 
-    def __exit__(self, exc_type, exc_value, traceback) -> bool:
+    def __exit__(self, exc_type, exc_value, traceback) -> Optional[bool]:
         return self.conn.__exit__(exc_type, exc_value, traceback)
 
     # Proxy through any unknown lookups to the DB conn class.

synapse/storage/types.py

@@ -12,7 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from typing import Any, Iterable, Iterator, List, Tuple
+from typing import Any, Iterable, Iterator, List, Optional, Tuple
 
 from typing_extensions import Protocol
 
@@ -65,5 +65,5 @@ class Connection(Protocol):
     def __enter__(self) -> "Connection":
         ...
 
-    def __exit__(self, exc_type, exc_value, traceback) -> bool:
+    def __exit__(self, exc_type, exc_value, traceback) -> Optional[bool]:
         ...