Use lib.overrideDerivation instead of <pkg>.overrideDerivation
to fix the evaluation of
python3Packages.pythonCatchConflictsHook.tests.catches-conflict-multiple-chains,
as buildPythonPackage and buildPythonApplication no longer provide
<pkg>.overrideDerivation
Clean up the leftover of commit 58bfe74123 ("buildPython*:
Deprecate and remove (buildPython* { ... }).override")
Add a test where a conflicting package can be found at the end of
multiple dependency chains. This is far too simple an example to
demonstrate the ill effects of exponential time complexity, but does
serve to demonstrate how the error output changes when each path is only
visited once.
