fix(types): change types for useMutation context in onSuccess (#3654)

changes context to optional in onSuccess callback

Author: Sunil Hari

src/core/mutation.ts

@@ -178,7 +178,7 @@ export class Mutation<
         this.options.onSuccess?.(
           data,
           this.state.variables!,
-          this.state.context!
+          this.state.context
         )
       )
       .then(() =>

src/core/types.ts

@@ -548,7 +548,7 @@ export interface MutationOptions<
   onSuccess?: (
     data: TData,
     variables: TVariables,
-    context: TContext
+    context: TContext | undefined
   ) => Promise<unknown> | void
   onError?: (
     error: TError,