Fix issues and add tests for Danish language

[fjerhammer]

Pull Request Checklist

• [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!).
• [ ] 📚 Updated documentation for changed code.
• [x] ⏩ Code is up-to-date with the master branch.

Description of Changes

Changes for Danish locale:

• Correct typos for relative humanizations.
• Use correct ordinal number format.
• Add tests.

[codecov[bot]]

Codecov Report

Merging #1091 (6891abb) into master (f8a6521) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1091   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2241      2243    +2     
  Branches       439       439           
=========================================
+ Hits          2241      2243    +2     

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

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