Fix usage of undeclared InvalidSysrootError

That error was not defined and triggered an Exception in the Exception.
It was not raised either. Use SysrootManagerError instead

Apertis: https://phabricator.apertis.org/T3777



Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>
Reviewed-by: Emanuele Aina <emanuele.aina@collabora.com>
Differential Revision: https://phabricator.apertis.org/D6402