package/python-lmdb: bump to version 0.99

This version fix the runtime issue with python 3.9 since _Py_ForgetReference()
was removed from the limited C API [1].

$ python sample_python_crossbar.py
/usr/bin/python3.9: symbol '_Py_ForgetReference': can't resolve symbol

python-lmbd 0.99 contain a refactoring removing _Py_ForgetReference()
from the code.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/830981961
https://gitlab.com/buildroot.org/buildroot/-/jobs/830981979

[1] https://docs.python.org/3/whatsnew/3.9.html#id3
[2] https://github.com/jnwatson/py-lmdb/commit/22a3724bdcda62853e8a250094f512eb20abe01f



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>