[BUGFIX] Invalid download URL for RestTools

When fetching ExtendingSphinxForTYPO3, the regular expression used to
detect the source link is wrong (searches for "snapshot" instead of the
actual "tar.gz"), preventing the extension from being installed.

This patch corrects the regular expression so that downloading and
installing the tools work again.

Fixes: #57997
Change-Id: I1266385d877c911eb13a7c16a553171b2f867deb
Reviewed-on: https://review.typo3.org/29552
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers