Mutation cache invalidation is broken in typescript

[mikecousins]

Describe the bug
Using the example code for mutation query invalidation now throws typescript errors.

To Reproduce
Steps to reproduce the behavior:

1. Add the sample code from the docs on mutation query invalidation
2. Typescript yells at you

Expected behavior
A clean build

Screenshots

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Edge
• Version: Latest

[boschni]

Created a fix in #1033