test PR, changed python versions listed for testing

[joshqsumner]

Describe your changes
Changed installation.md file to say it tests python 3.8, 3.9, and 3.10

Type of update

• Update to docs

Associated issues
#999

Additional context
No additional context

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

[codecov]

Codecov Report

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The diff coverage is n/a.

❗ Current head 57ae2da differs from pull request most recent head 6cc5575. Consider uploading reports for the commit 6cc5575 to get more accurate results

@@           Coverage Diff           @@
##             main    #1015   +/-   ##
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  Coverage        ?   99.98%           
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  Files           ?      141           
  Lines           ?     6004           
  Branches        ?        0           
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  Hits            ?     6003           
  Misses          ?        1           
  Partials        ?        0           

Flag	Coverage Δ
unittests	99.98% <ø> (?)

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