[stable6] Update SabreDAV to 1.7.11

:no_entry: NOMERGE :no_entry: 

DON'T merge before 6.0.2 is released.

Backport of c77c4ddbd4ae86a307d073647e76d602eafd0c64 to stable6

@DeepDiver1975 as discussed.

Are the autoloader changes necessary for that update ?