Built in discovery class is always preferred over plugin supplied classes

[AWhetter]

• ran the linter to address style issues (tox -e fix_lint)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

This ensures that the builtin Discovery class is always chosen over any discovery class provided by plugins, as discussed in #2087

Closes #2087

[AWhetter]

These lines have been borrowed from here:

virtualenv/src/virtualenv/run/plugin/creators.py

Lines 52 to 53 in 0262fa6

	# prefer the built-in venv if present, otherwise fallback to first defined type
	choices = sorted(choices, key=lambda a: 0 if a == "builtin" else 1)

[codecov]

Codecov Report

Merging #2088 (e25f2bc) into main (0262fa6) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #2088      +/-   ##
==========================================
- Coverage   93.70%   93.56%   -0.14%     
==========================================
  Files          88       88              
  Lines        4383     4385       +2     
==========================================
- Hits         4107     4103       -4     
- Misses        276      282       +6     

Flag	Coverage Δ
tests	93.56% <100.00%> (-0.14%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/virtualenv/run/plugin/discovery.py	100.00% <100.00%> (ø)
...ualenv/create/via_global_ref/builtin/pypy/pypy2.py	92.20% <0.00%> (-6.50%)	⬇️
src/virtualenv/util/path/_pathlib/via_os_path.py	89.62% <0.00%> (-1.89%)	⬇️
src/virtualenv/util/path/_pathlib/__init__.py	96.96% <0.00%> (+3.03%)	⬆️

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[AWhetter]

This code coverage report looks incorrect? The coverage has not reduced this much and I got a similar result when I made a change that didn't touch the code in #2089

[gaborbernat]

[gaborbernat]

Released via https://pypi.org/project/virtualenv/20.4.4/