Fixed arrow.get with a timestamp and a timezone string

[jadchaar]

Pull Request Checklist

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

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

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

Fixed arrow.get with a timestamp and a timezone string.

[codecov-io]

Codecov Report

Merging #744 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #744   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           9      9           
  Lines        1678   1679    +1     
  Branches      283    285    +2     
=====================================
+ Hits         1678   1679    +1

Impacted Files	Coverage Δ
arrow/util.py	100% <ø> (ø)	⬆️
arrow/arrow.py	100% <100%> (ø)	⬆️

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