Docs for set_site_transient() says max length of transient name is 40, it's actually 167

[jdgrimes]

In [28735] the docs were added, and in [34030] the length of the option_name column was lengthened. The docs for set_transient() were updated in [34045], but set_site_transient() was missed.

The length of the option_name column was updated to 191, but 24 characters are taken up by prefixing the transient name with _site_transient_timeout_ when the timeout is saved. 191 - 24 = 167.

[lukecavanagh]

Basic patch

[SergeyBiryukov]

In 40432:

Docs: Update the length limit in set_site_transient() docs after [34030].

Props lukecavanagh, jdgrimes.
Fixes #40455.