And when running srssync, return early if the version number is unchanged
from the last run.
This avoids running the full (slow, on proj 6 builds) srssync with
every build, which is PITA for rapid development...
It's too dangerous to reuse the existing one, as it breaks the
ability to run multiple versions of qgis (i.e. proj < 6 and proj >= 6)
on the same machine
Fixes#30569
