fix(typescript-urql-graphcache): improve typing

[dargmuesli]

Which packages are impacted by your issue?

@graphql-codegen/typescript-urql-graphcache

Describe the bug

Your Example Website or App

n/a

Steps to Reproduce the Bug or Issue

Run eslint.

Expected behavior

No lint errors.

Screenshots or Videos

No response

Platform

n/a

Codegen Config File

No response

Additional context

I'll submit the fix in a PR right away:

• fix(typescript-urql-graphcache): improve typing #1110