Update open_url test to use self hosted image

[nfahlgren]

Describe your changes
Updates the test for open_url to use a self-hosted image. The original test opens an image in GitHub and is now triggering a too many attempts error.

Type of update
Is this a: Bug fix

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]

DeepSource Code Review

We reviewed changes in 12eb31d...f0e8dbf on this pull request. Below is the summary for the review, and you can see the individual issues we found as inline review comments.

See full review on DeepSource ↗

PR Report Card

Overall Grade

Security   Reliability   Complexity   Hygiene   Coverage

Code Review Summary

Analyzer	Status	Updated (UTC)	Details
Python		Mar 15, 2026 9:16p.m.	Review ↗
Test coverage		Mar 15, 2026 9:16p.m.	Review ↗

Code Coverage Summary

Language	Line Coverage (New Code)	Line Coverage (Overall)
Aggregate	100% [✓ above threshold]	100%
Python	100% [✓ above threshold]	100%

➟ Additional coverage metrics may have been reported. See full coverage report ↗

[joshqsumner]

Looks good!