Remove Sphinx pinning

[QuLogic]

This was pinned in #434 because of the RTD theme, but #485 switched to the pydata sphinx theme, so there should not be any issues.

Fixes #435

TODO:

• Unit tests and/or doctests in docstrings
• [n/a] Tests pass locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.91%. Comparing base (9617e6f) to head (94c2bf1).
Report is 53 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #552   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files          59       59           
  Lines        2339     2339           
=======================================
  Hits         2337     2337           
  Misses          2        2