Update Autorest to 6.13.16

[danaelhe]

Addresses #290

Was able to reproduce the issue described in #290 with docstring errors with python 3.12:

make generate
.....
<unknown>:34822: SyntaxWarning: invalid escape sequence '\ '
<unknown>:42159: SyntaxWarning: invalid escape sequence '\ '
<unknown>:48460: SyntaxWarning: invalid escape sequence '\ '
<unknown>:63275: SyntaxWarning: invalid escape sequence '\ '
<unknown>:63370: SyntaxWarning: invalid escape sequence '\ '
<unknown>:75107: SyntaxWarning: invalid escape sequence '\ '

Thanks to @onlined who let us know this was fixed in autorest 6.13.16

Updated the autorest version to 6.13.16 and ran make generate

Had to also update the python version in pyproject.toml to ^3.9.0 [tool.poetry.dependencies] to fix the issue - Installing frozenlist (1.3.3): Failed when running poetry install.

It's probably due time to update to a newer version of autorest.