CI run against latest deps is failing

[github-actions]

See https://github.com/matrix-org/synapse/actions/runs/2493388697

[DMRobertson]

synapse/config/server.py:771: error: Unsupported operand types for + ("bytes" and "str")  [operator]

[DMRobertson]

synapse/synapse/config/server.py

Lines 767 to 773 in 28989cb

	if listeners:
	# comment out this block
	unsecure_http_bindings = "#" + re.sub(
	"\n {10}",
	lambda match: match.group(0) + "#",
	unsecure_http_bindings,
	)

Not sure I understand what the error is here. Does mypy suddenly think that match.group(0) is a bytes?

[DMRobertson]

The stubs on typeshed should select the first overload because "\n {10}": str, see https://github.com/python/typeshed/blob/master/stdlib/re.pyi#L136-L146

[DMRobertson]

I can reproduce this after pip install mypy==0.961 mypy-zope==0.38 on top of the current poetry.lock.

[DMRobertson]

I'm guessing we only saw this now because mypy-zope has just made a release supporting a version newer than mypy 0.950.

[DMRobertson]

I think the line that's being complained about is due for removal in #12941. I'll assume that fixes this problem and let that PR close this issue. CI will open a new issue if my assumption is wrong!