URL Checker: resolve failure checking PLY documentation

[jsiirola]

Fixes # .

Summary/Motivation:

The URL checker has started failing for the PLY documentation page due to a certificate trust issue. This switches the URL from https to http to avoid that failure.

Changes proposed in this PR:

• use http instead of https for PLY documentation

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• AI tools contributed to the development of this PR

  • AI tools generated documentation (including the PR description/comments, code comments, and/or Sphinx documentation)
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  • AI tools generated code (apart from tests)

  Review process (select ONE):

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    • Added and ran tests
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  • As-is: AI-generated content was commited directly to the repository

Notes for reviewers (optional):

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By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.66%. Comparing base (b953cf9) to head (8ea8fe7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4004      +/-   ##
==========================================
- Coverage   90.13%   89.66%   -0.48%     
==========================================
  Files         917      917              
  Lines      109101   109101              
==========================================
- Hits        98343    97828     -515     
- Misses      10758    11273     +515     

Flag	Coverage Δ
builders	29.09% <ø> (+0.01%)	⬆️
default	86.13% <ø> (?)
expensive	35.07% <ø> (?)
linux	72.34% <ø> (-17.30%)	⬇️
linux_other	72.34% <ø> (-15.33%)	⬇️
oldsolvers	27.91% <ø> (-0.12%)	⬇️
osx	83.11% <ø> (+<0.01%)	⬆️
win	?

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