Can voltage regulators deal with negative output current?
Looking at its internal schematic, 7805 doesn't have a push pull output, only one pass transistor (outlined in yellow) so it can't sink current.

Generally manufacturers won't waste silicon area on a power transistor that is not used in the application, so most voltage regulators don't have this feature.
Regulators that do have this feature are, for example: shunt regs, DDR termination regs, and synchronous buck regulators (forced PWM mode is probably required).