Rollup merge of #91065 - wesleywiser:add_incr_test, r=jackh726

Rollup merge of #91065 - wesleywiser:add_incr_test, r=jackh726

Add test for evaluate_obligation: Ok(EvaluatedToOkModuloRegions) ICE

Adds the minimial repro test case from #85360. The fix for #85360 was
supposed to be #85868 however the repro was resolved in the 2021-07-05
nightly while #85868 didn't land until 2021-09-03. The reason for that
is d34a3a401b4e44f289a4d5bf53da83367cbb6aa7 **also** resolves that
issue.

To test if #85868 actually fixes #85360, I reverted
d34a3a401b4e44f289a4d5bf53da83367cbb6aa7 and found that #85868 does
indeed resolve #85360.

With that question resolved, add a test case to our incremental test
suite for the original Ok(EvaluatedToOkModuloRegions) ICE.

Thanks to ````@lqd```` for helping track this down!