Fix: expiration ttl as timedelta on gcpubsub

[j0j1j2]

With protobuf version 5.29.3, ttl value as string is not supported.

[auvipy]

why the PR was closed?

[j0j1j2]

I was using poetry and I met this error with protobuf 5.xx. So I created this PR to fix this error.
but after few minutes later I found that in requirements/extras/gcpubsub.txt, the protobuf version is specified to 4.25.5.
My PR works on protobuf version 5.29.3. but I cannot assure it works on protobuf 4.25.5, So I closed this issue.
If you want to open this again, I'll reopen this PR.

[auvipy]

we will need to update the version in future versions