When a slider operator has only a single 'slider property', disregard
Tab keyboard events.
This fixes an issue where the Tab key would make the slider operator
misbehave in a way that required cancelling the operator and re-starting
it.
Context: Depending on the specific operator, Tab can be used to toggle
between different parameters. The generic handler for modal slider
operators didn't take this into account, though, and passed through the
Tab key to the rest of Blender, when it wasn't handled by the specific
operator.
Pull Request: https://projects.blender.org/blender/blender/pulls/120922