[processing] Correctly supress CRS selector dialog when testing

input layer validity

TODO: we NEED a non-hacky way to supress this dialog and allow
invalid CRS for layers!

Fixes #17948

src/core/processing/qgsprocessingutils.cpp

@@ -141,7 +141,7 @@ class ProjectionSettingRestorer
     {
       QgsSettings settings;
       previousSetting = settings.value( QStringLiteral( "/Projections/defaultBehavior" ) ).toString();
-      settings.setValue( QStringLiteral( "/Projections/defaultBehavior" ), QString() );
+      settings.setValue( QStringLiteral( "/Projections/defaultBehavior" ), QStringLiteral( "useProject" ) );
     }
 
     ~ProjectionSettingRestorer()