"cannot be used to index type" error when indexing `NonNullable` of a generic type in typescript 4.8

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Bug Report

🔎 Search Terms

4.8 nonnullable cannot be used to index type

🕗 Version & Regression Information

4.8.0-dev.20220624

• This changed between versions 4.7.4 and 4.8-beta

⏯ Playground Link

Playground link with relevant code

💻 Code

type Foo = { [key: string]: unknown }
type NullableFoo = Foo | undefined

type Bar<T extends NullableFoo> = NonNullable<T>[string] //error on 4.8, no error on 4.7

type Baz<T extends Foo> = NonNullable<T>[string] // no error
type Qux = NonNullable<NullableFoo>[string] // no error

🙁 Actual behavior

Type 'string' cannot be used to index type 'NonNullable'.(2536)

🙂 Expected behavior

no error