Fix Typos in Storage Items

[JohnReedV]

Describe the bug

A few storage items such as LastMechansimStepBlock & PendingdHotkeyEmission are misspelled.

To Reproduce

https://github.com/opentensor/subtensor/blob/4f3f151ce940faded957496fe3b02191aa322ffb/pallets/subtensor/src/lib.rs#L757

Expected behavior

All pallet items should be spelled correctly.

Screenshots

No response

Environment

Linux

Additional context

No response