Most wall-warts are unregulated, and will output more than the rated voltage
until you place a load on them. The LM7805 should still work just fine with this
however since most flavors are rated up to around 35V MAX input.

22V input shouldn't do much more than make your regulator run much hotter. It
should still work fine.

Are you 100% sure you don't have an LM7809 stuck in there, or maybe have
your LM7805 wired in backwards? 8.7V out from an LM7805 is not good.