Fix up some typechecking (#6150)

.gitignore

changelog.d/6150.misc

synapse/api/errors.py

synapse/api/room_versions.py

synapse/app/_base.py

synapse/config/appservice.py

synapse/config/consent_config.py

synapse/config/password_auth_providers.py

synapse/config/repository.py

synapse/config/server.py

synapse/config/server_notices_config.py

synapse/logging/opentracing.py

synapse/logging/utils.py

synapse/metrics/__init__.py

synapse/metrics/_exposition.py

synapse/python_dependencies.py

synapse/types.py

synapse/util/async_helpers.py

synapse/util/caches/__init__.py

synapse/util/caches/descriptors.py