Update Finnish locale

[aivot-on]

Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

• [x] 🧪 Added tests for changed code.
• [x] 🛠️ All tests pass when run locally (run tox or make test to find out!).
• [x] 🧹 All linting checks pass when run locally (run tox -e lint or make lint to find out!).
• [x] 📚 Updated documentation for changed code.
• [x] ⏩ Code is up-to-date with the master branch.

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Description of Changes

Update the Finnish localization to use the correct declension for singular second and day, and remove the "muutama" from the plural seconds which seems to be old mishap with localization.

[codecov[bot]]

Codecov Report

Merging #1119 (aa86264) into master (8d9ae23) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1119   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2325      2325           
  Branches       449       449           
=========================================
  Hits          2325      2325           

Impacted Files	Coverage Δ
arrow/locales.py	100.00% <ø> (ø)

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