Fix a few compiler warnings

[jmcarcell]

PySys_SetArgv is deprecated since Python 3.11 (see https://docs.python.org/3/c-api/init.html#c.PySys_SetArgv). The recommended way can be found here. I also removed a couple of checks for Python 3.

BEGINRELEASENOTES

• Fix warnings related to unused variables and shadowing of already existing variables
• Don't use the deprecated PySys_SetArgv

ENDRELEASENOTES

[github-actions]

Test Results

   14 files     14 suites   6h 30m 59s ⏱️
  363 tests   363 ✅ 0 💤 0 ❌
2 496 runs  2 496 ✅ 0 💤 0 ❌

Results for commit 87dc486.