[prerelease] `ExceptionInfo.traceback[...].path` changed from py.path to pathlib.Path

[The-Compiler]

As for the ExceptionInfo.traceback[...].path one: The PR looks good, but it seems to me that we should retain and perhaps deprecate the path attribute properly, instead of (more or less silently) replacing it, despite it being public API)?

Originally posted by @The-Compiler in #9415 (reply in thread)

[nicoddemus]

Can we assess the impact of path of the change from py.path.local to pathlib.Path? If it doesn't break the world, just adding a good note about it in the changelog might be sufficient. I suspect this is rarely used, with a trivial fix, so it might save us time and effort if we can avoid a deprecation cycle.

[The-Compiler]

At least a quick search seems to suggest that this is only an issue for promise indeed - so perhaps we should go ahead and just add that to the changelog and deprecation docs instead then?

[bluetech]

We've decided to accept this breaking change. Will send a PR to update the changelog.