tests: new codespell, narrowed checks and better execution order

[sergiusens]

• Run mypy first and only then do spell checking.
• Update codespell to 0.12.0 which has better detection.
• Fix spelling issues discovered by codespell.
• Narrow down the list of directories searched for (no need to look in
  e.g.; parts).

Signed-off-by: Sergio Schvezov sergio.schvezov@canonical.com

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• If this is a bugfix. Have you checked that there is a bug report open for the issue you are trying to fix on bug reports?
• If this is a new feature. Have you discussed the design on the forum?
• Have you successfully run ./runtests.sh static?
• Have you successfully run ./runtests.sh unit?

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[kyrofa]

Yes, thank you, I've had to fix some of these items locally as well, now I don't need to propose them.

[codecov-io]

Codecov Report

Merging #2162 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2162      +/-   ##
==========================================
- Coverage   91.19%   91.18%   -0.01%     
==========================================
  Files         198      198              
  Lines       12471    12471              
  Branches     1846     1846              
==========================================
- Hits        11373    11372       -1     
  Misses        742      742              
- Partials      356      357       +1

Impacted Files	Coverage Δ
snapcraft/internal/project_loader/_config.py	99.52% <ø> (ø)	⬆️
snapcraft/plugins/ruby.py	98.79% <ø> (ø)	⬆️
snapcraft/project/_project_options.py	89.23% <ø> (ø)	⬆️
snapcraft/plugins/kernel.py	94.11% <ø> (ø)	⬆️
...apcraft/internal/build_providers/_base_provider.py	100% <ø> (ø)	⬆️
snapcraft/internal/elf.py	82.84% <0%> (-0.33%)	⬇️

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