Install dependencies for display testing

[nfahlgren]

Describe your changes
Updates GitHub Actions CI workflow to install dependencies for handling tests that open displays

Type of update
Is this a: Work in progress

For the reviewer
See this page for instructions on how to review the pull request.

• PR functionality reviewed in a Jupyter Notebook
• All tests pass
• Test coverage remains 100%
• Documentation tested
• New documentation pages added to plantcv/mkdocs.yml
• Changes to function input/output signatures added to updating.md
• Code reviewed
• PR approved

[deepsource-io]

Here's the code health analysis summary for commits 19da7e5..120bc72. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Python	✅ Success		View Check ↗
Test coverage	❌ Failure	❗ 3 occurences introduced	View Check ↗

Code Coverage Report

Metric	Aggregate	Python
Branch Coverage	100%	100%
Composite Coverage	66.7% (down 33.3% from main)	66.7% (down 33.3% from main)
Line Coverage	66.7% (down 33.3% from main)	66.7% (down 33.3% from main)
New Branch Coverage	100%	100%
New Composite Coverage	64.9%	64.9%
New Line Coverage	64.9%	64.9%

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