Track changes in PyPy behavior introduced in 7.3.14

[jsiirola]

Fixes # .

Summary/Motivation:

PyPy 7.3.14 changed how inspect behaves to diverge from CPython's behavior (see pypy/pypy#4839). This introduced a test failure in Pyomo. This PR resolves the test failure, by acknowledging that PyPy and CPython behave differently (and does NOT introduce hacks into Pyomo to make both platforms behave similarly)

Changes proposed in this PR:

• Update tests to recognize / document that we will see different behavior on recent PyPy
• Standardize the check of running under PyPy in other tests

Legal Acknowledgement

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[mrmundt]

I appreciate the explanatory comments. Also, this is annoying.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d04f6bb) 88.10% compared to head (131fd3f) 88.09%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3087      +/-   ##
==========================================
- Coverage   88.10%   88.09%   -0.01%     
==========================================
  Files         775      775              
  Lines       91549    91549              
==========================================
- Hits        80660    80652       -8     
- Misses      10889    10897       +8     

Flag	Coverage Δ
linux	85.46% <ø> (ø)
osx	75.47% <ø> (ø)
other	85.64% <ø> (ø)
win	82.80% <ø> (-0.01%)	⬇️

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