Auto merge of #56391 - alexcrichton:less-compare-mode, r=Mark-Simulacrum

ci: Only run compare-mode tests on one builder

The run-pass test suite currently takes 30 minutes on Windows, and
that appears to be roughly split between two 15 minute runs of the test
suite: one without NLL and one with NLL. In discussion on Discord the
platform coverage of the NLL compare mode may not necessarily be worth
it, so this commit removes the NLL compare mode from tests by default,
and then reenables it on only one builder.