Bump required python version to 3.9

Summary:
Attempt to run unit tests with python 3.8 (ondemand default) fails with:

ImportError: PyO3 modules compiled for CPython 3.8 or older may only be initialized once per interpreter process

PyO3 [1] seems to be a transitive dependency.

The easiest way to fix this is to upgrade underlying python.

[1] https://pyo3.rs/v0.24.2/getting-started.html

Reviewed By: danielocfb, anakryiko

Differential Revision: D74443235

fbshipit-source-id: 2577b78d8b6fb3452af9040b6cbc74101e6f7103

Author: theihor

pyproject.toml

@@ -22,7 +22,7 @@ aiohttp = "^3.8"
 aiohttp-retry = "^2.8"
 aioresponses = "^0.7"
 multidict = "^6.0"
-python = "^3.8"
+python = "^3.9"
 cachetools = "^5.3.0"
 gitpython = "^3.1"
 opentelemetry-api = "^1.18.0"