Update pinned requirements and pin pygments == 2.18.0 due to incompatibility with sphinx-codeautolink - #2933

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.49%. Comparing base (87a0193) to head (953c175).
Report is 123 commits behind head on main.

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- Coverage   95.28%   94.49%   -0.79%     
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  Files         108      108              
  Lines        9631     9631              
  Branches     1451     1451              
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- Hits         9177     9101      -76     
- Misses        273      343      +70     
- Partials      181      187       +6     

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There seem to be two issues that have arisen here...a great way to return from a month long vacation! 😺

1. For the documentation build, we're getting a bunch of errors like:

   /home/runner/work/PlasmaPy/PlasmaPy/docs/contributing/coding_guide.rst: WARNING: Could not match transformation of `plasmapy.particles` on source lines 1-1, source:
   from plasmapy.particles import particle_input, ParticleLike
   
   @particle_input
   def f(particle: ParticleLike) -> Particle | CustomParticle | ParticleList:
       return particle  # type: ignore[return-value]
   /home/runner/work/PlasmaPy/PlasmaPy/docs/contributing/coding_guide.rst: WARNING: Could not match transformation of `astropy.units` on source lines 1-1, source:
   import astropy.units as u
   from plasmapy.utils.decorators import validate_quantities

   I think this may have something to do with this section of the doc troubleshooting guide which I completely forgot about?

   This may be a result of a new version of pygments not being compatible with sphinx-codeautolink.

2. There's a change in the output for scipy.optimize.fsolve which affects a doctest for the fit functions. [fixed]

Figured it out! The Could not match transformation of errors occurred because the newest version of pygments (v2.19.1) is incompatible with sphinx-codeautolink.