import tomli as tomllib for docs builds before Python 3.11

[zacharyburnett]

tomli is implemented read-only as tomllib in Python 3.11

Checklist

• added entry in CHANGES.rst under the corresponding subsection
• updated relevant tests
• updated relevant documentation
• updated relevant milestone(s)
• added relevant label(s)

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.83 ⚠️

Comparison is base (96fb108) 63.67% compared to head (f4fa6b0) 62.84%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #657      +/-   ##
==========================================
- Coverage   63.67%   62.84%   -0.83%     
==========================================
  Files          78       78              
  Lines        4113     4113              
==========================================
- Hits         2619     2585      -34     
- Misses       1494     1528      +34     

Flag	Coverage Δ		*Carryforward flag
nightly	56.66% <ø> (-6.96%)	⬇️	Carriedforward from 3a43351

*This pull request uses carry forward flags. Click here to find out more.

see 6 files with indirect coverage changes

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