Tests: uncover a quirk in our linkcheck tests

[jayaddison]

Purpose

This change only affects our test suite; it exposes a quirk in behaviour as a result of an event-based call to the compile_linkcheck_allowed_redirects method (a fairly self-descriptive method).

This is a limitation of our linkcheck testsuite; some test cases may unwittingly rely on the compilation step.

Had this compilation been in place - reflecting how a sphinx-build -b linkcheck ... session would usually proceed -- then tests would have begun failing with the merge of #13452.

I think it suggests an unexpected change-in-default behaviour; confirming that tests fail for this PR could help to demonstrate the problem and discuss it.

References

• Discovered during investigation of Possible regression in linkcheck_allowed_redirects default following PR 13452 #13462.
• Relates to Warn on all redirects if linkcheck_allowed_redirects is an empty dictionary #13452.