docs: Modify onMutate signature to add context parameter (#9982)

Updated the onMutate function signature to include context.

Author: RND332

docs/framework/react/reference/useMutation.md

@@ -64,7 +64,7 @@ mutate(variables, {
   - Optional
   - defaults to `'online'`
   - see [Network Mode](../guides/network-mode.md) for more information.
-- `onMutate: (variables: TVariables) => Promise<TOnMutateResult | void> | TOnMutateResult | void`
+- `onMutate: (variables: TVariables, context: MutationFunctionContext) => Promise<TOnMutateResult | void> | TOnMutateResult | void`
   - Optional
   - This function will fire before the mutation function is fired and is passed the same variables the mutation function would receive
   - Useful to perform optimistic updates to a resource in hopes that the mutation succeeds