chore: Update to nbQA v0.5.6 in pre-commit

[pre-commit-ci]

* [pre-commit.ci] pre-commit autoupdate
   - Update nbQA to v0.5.6

[codecov]

Codecov Report

Merging #1240 (f3bc7a0) into master (fd7930c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1240   +/-   ##
=======================================
  Coverage   97.45%   97.45%           
=======================================
  Files          63       63           
  Lines        3700     3700           
  Branches      524      524           
=======================================
  Hits         3606     3606           
  Misses         55       55           
  Partials       39       39           

Flag	Coverage Δ
unittests	97.45% <ø> (ø)

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