Starting from python3.11 inspect.formatargspec was removed:

    f = <function test_func.<locals>.zzz at 0x7fb6d265fec0>

        def fmtargspec(f): # -> str
            with warnings.catch_warnings():
                warnings.simplefilter('ignore', DeprecationWarning)
    >           return inspect.formatargspec(*inspect.getargspec(f))
    E           AttributeError: module 'inspect' has no attribute 'formatargspec'

    golang/golang_test.py:1823: AttributeError

We were already handling formatargspec deprecation in 45f4df9e (golang:
tests: Silence inspect deprecation warning), but now is the time to
actually replace its usage.

-> Fix it by using `str(inspect.signature(f))` instead of
   `inspect.formatargspec(*inspect.getargspec(f))`.