Add trivial impl of Borrow<str> for Atom

[adamreichold]

This enables Atom to be used in methods like HashMap::entry_ref.

[jdm]

@bors-servo r+ Thanks!

[bors-servo]

:pushpin: Commit 13db052 has been approved by jdm

[bors-servo]

:hourglass: Testing commit 13db052daf2f737de8cc63dd4dd73b291b5e630e with merge 362ba45bb97a2ed3abf4a1ffa97774845c2954e2...

[bors-servo]

:broken_heart: Test failed - checks-github

[adamreichold]

I committed a Cargo lockfile which references once_cell 1.14.0 instead of the current 1.16.0 and should be compatible with the MSRV of 1.49.0. I also adjust the CI workflow to use this lockfile when testing Rust 1.49.0 in the CI even I am not completely sure whether this will work for all parts of the CI workflow.

[jdm]

Oh, if the build failed it's because one of our dependencies now has a minimum Rust version that's higher than our version. There's nothing we can do about that except pin the older version in our dependencies, or update our MSRV. We just update our MSRV in that case.

[jdm]

https://github.com/servo/string-cache/pull/267

[adamreichold]

267

I rebased on the post-merge master branch. I have to admit that I would not have bumped MSRV to follow once_cell as said project has apparently dropped the notion of keeping an MSRV.

[jdm]

@bors-servo r+

[bors-servo]

:pushpin: Commit 37b459f has been approved by jdm

[bors-servo]

:hourglass: Testing commit 37b459f8ce1ec694e8218ebdeef30c06f68e6205 with merge 6c044c91bb3d8212dae931152a7895f498574f71...

[bors-servo]

:sunny: Test successful - checks-github Approved by: jdm Pushing 6c044c91bb3d8212dae931152a7895f498574f71 to master...