Update grayscale_tutorial.md

[zeeuqsze]

Describe your changes Updated Colab button

Type of update Is this a:

• Update to documentation

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[bot]]

Here's the code health analysis summary for commits 1dbebaf..4b50aa2. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Python	✅ Success		View Check ↗
Test coverage	✅ Success		View Check ↗

Code Coverage Report

Metric	Aggregate	Python
Branch Coverage	100%	100%
Composite Coverage	100%	100%
Line Coverage	100%	100%

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