fix variance/sigma bug

[ztq1996]

qp norm takes sigma, not variance

Code Quality

• My code follows the code style of this project
• I have written unit tests or justified all instances of #pragma: no cover; in the case of a bugfix, a new test that breaks as a result of the bug has been added
• My code contains relevant comments and necessary documentation for future maintainers; the change is reflected in applicable demos/tutorials (with output cleared!) and added/updated docstrings use the NumPy docstring format
• Any breaking changes, described above, are accompanied by backwards compatibility and deprecation warnings

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.39%. Comparing base (5860497) to head (743abaa).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #22   +/-   ##
=======================================
  Coverage   64.39%   64.39%           
=======================================
  Files           2        2           
  Lines         514      514           
=======================================
  Hits          331      331           
  Misses        183      183           

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[sschmidt23]

Thanks for catching this, looks good.