Fix `Filedialog` to work across (mac)OS

Description

Previously, we would use the directory keyword occasionally when calling certain FileDialog methods. The directory keyword is not able to be used on macOS, but the dir keyword seems to work well across all OS's (Windows, Mac, and Linux).

This PR substitutes the directory keyword with dir instead when calling FileDialog methods.

No automated tests, but manually tested the Save Configuration button on all three OS's.

Types of changes

[x] Bugfix
[ ] New feature
[ ] Refactor / Code style update (no logical changes)
[ ] Build / CI changes
[ ] Documentation Update
[ ] Other (explain)

Does this address any currently open issues?

1251

Outside contributors checklist

[ ] Review the guidelines for contributing to this repository
[ ] Read and sign the CLA and add yourself to the authors list
[ ] Make sure you are making a pull request against the develop branch (not main). Also you should start your branch off develop
[ ] Add tests that prove your fix is effective or that your feature works
[ ] Add necessary documentation (if appropriate)

Thank you for contributing to SLEAP!

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Codecov Report

:exclamation: No coverage uploaded for pull request base (develop@1c2be11). Click here to learn what that means. The diff coverage is 76.00%.

@@            Coverage Diff             @@
##             develop    #1393   +/-   ##
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  Coverage           ?   72.73%           
==========================================
  Files              ?      133           
  Lines              ?    23718           
  Branches           ?        0           
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  Hits               ?    17252           
  Misses             ?     6466           
  Partials           ?        0

Impacted Files	Coverage Δ
sleap/gui/dialogs/formbuilder.py	`90.02% <0.00%> (ø)`
sleap/gui/learning/dialog.py	`67.72% <0.00%> (ø)`
sleap/gui/dialogs/filedialog.py	`54.16% <86.36%> (ø)`

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talmolab / sleap