const functions like get() returns mutable type in Ref/RefPtr. Do the same in CheckedRef/CheckedPtr.
Pull request: https://github.com/WebKit/WebKit/pull/17313
Committed 267543@main (643f0a10c60b): <https://commits.webkit.org/267543@main> Reviewed commits have been landed. Closing PR #17313 and removing active labels.
<rdar://problem/114805280>