It doesn't seem to be supported at the moment (executing it with a
tenant-enabled Firebase project yields an
`UNSUPPORTED_TENANT_OPERATION`) error, but once it _is_ supported,
this library will need no or just minimal updates.

The Firebase Admin SDK for PHP has integration tests checking for this
error so that we know early on when it starts working.

Co-authored-by: Tomy Kho <mail@tomykho.dev>

The new library provides an implementation of the not yet released
PSR-20 Clock interface and is maintained by the same guy who maintains
the old one: me ^^