Downgrade doc8 dependency

[gadomski]

Related Issue(s): None

Description:

The v1 of doc8 was breaking dependency resolution:

ERROR: Cannot install -r ./requirements-docs.txt (line 2), -r ./requirements-docs.txt (line 4), -r ./requirements-docs.txt (line 5), -r ./requirements-docs.txt (line 6) and -r ./requirements-test.txt (line 9) because these package versions have conflicting dependencies.

The conflict is caused by:
    sphinx 4.5.0 depends on docutils<0.18 and >=0.14
    nbsphinx 0.8.9 depends on docutils
    pydata-sphinx-theme 0.8.1 depends on docutils!=0.17.0
    sphinx-panels 0.6.0 depends on docutils
    doc8 1.0.0 depends on docutils<0.21 and >=0.19

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)

[codecov-commenter]

Codecov Report

Merging #883 (2833be9) into main (25cdf9d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #883   +/-   ##
=======================================
  Coverage   94.32%   94.32%           
=======================================
  Files          83       83           
  Lines       11963    11963           
  Branches     1403     1403           
=======================================
  Hits        11284    11284           
  Misses        496      496           
  Partials      183      183           

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[gadomski]

Fixed by #897