[stubgen] infer_sig_from_docstring fails with python3.12 inline generic

Bug Report

Trying to infer types from docstrings with python3.12 inline generics fails to generate.

To Reproduce

from mypy.stubdoc import infer_sig_from_docstring
infer_sig_from_docstring('\nfunc[T, V](x: T, y: V) -> T', 'func')

Expected Behavior

infer_sig_from_docstring('\nfunc[T, V](x: T, y: V) -> T', 'func') ==
            [
                FunctionSig(
                    name="func", args=[ArgSig(name="x", type="T"), ArgSig(name="y", type="V")], ret_type="T"
                )
            ]

Actual Behavior

infer_sig_from_docstring('\nfunc[T, V](x: T, y: V) -> T', 'func') == []

Your Environment

• Mypy version used: 1.11.dev
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: python 3.10

Start at the mypy.stubdoc.infer_sig_from_docstring entry point and reproduce the issue with the supplied Python call using an inline generic signature. Done means the call returns one FunctionSig for func with x and y arguments and return type T, rather than an empty list.