Actions can be broken by changed compiler output

[smklein]

https://github.com/oxidecomputer/dropshot/pull/136/checks?check_run_id=3877374795 has an example

Paraphrasing from my comment elsewhere:

• We have some tests that check for "compiler failures" looking like we want
• I suspect the compiler changed, and the compiler output changed
• This change - though probably innocent - caused "expected != actual", and the test failed.

The only line that changed was actually part of the compiler message giving path hints:

Expected: ::: $WORKSPACE/dropshot/src/api_description.rs

vs

Actual: ::: src/api_description.rs:54:33

This is repro-d on a no-op change: #137

[smklein]

After noticing that #139 did not fix this, I tried #140.

I still think #139 is probably worthwhile doing, but this is another source of variability: dependencies. The issue wasn't a toolchain revision, but some dependency causing different output. I have not dug into the dependencies to figure out what caused this particular change.

[smklein]

Re-opening, as the potential for this issue still exists even with #140 merged.

#139 provides a long-term solution.