Seems like an unintended change.
It started in 12.0.0, that has the following "known issue" in its release notes:
An annotation causes spurious lint errors claiming
CredentialsClientare internal-only. These can safely be ignored.
Guess they weren't only for
CredentialsClient, but they fixed only those in 12.0.1:
Fixes issue that caused spurious Android lint errors claiming
The corresponding source code of
release() appears to be the same across versions 11.8.0-12.0.1, so i believe you can safely ignore these warnings.