fix(docs): use 'onchain' (cspell forbids 'on-chain')

Author: dbanks12

docs/docs-developers/docs/resources/migration_notes.md

@@ -74,7 +74,7 @@ Direct callers of the `SimulationOverrides` constructor must switch from a posit
 + new SimulationOverrides({ contracts });
 ```
 
-`overrides.contracts` swaps contract instances in the simulator's contract DB — useful for simulating a contract being on a different class than the one it was deployed with. To simulate a complete on-chain upgrade flow, use the `fastForwardContractUpdate` helper which returns a `SimulationOverrides` covering both registry storage rewrites and the upgraded instance entry:
+`overrides.contracts` swaps contract instances in the simulator's contract DB — useful for simulating a contract being on a different class than the one it was deployed with. To simulate a complete onchain upgrade flow, use the `fastForwardContractUpdate` helper which returns a `SimulationOverrides` covering both registry storage rewrites and the upgraded instance entry:
 
 ```typescript
 import { fastForwardContractUpdate } from '@aztec/aztec.js';