#3427 - Treat manifest warnings as warnings

[iBotPeaches]

// Whether validation errors should be treated only as warnings. If this is 'true', then an
// incorrect node will not result in an error, but only as a warning, and the parsing will
// continue.
bool warn_validation = false;

Missed this during aapt2 addition. We should have aapt2 in the least strict mode possible as we are rebuilding apps and shouldn't be binded by the latest in build-time enforcement from aapt2.

Fixes: #3427