[typescript-rtk-query] TypedDocumentString cast 'as unknown as string' causes runtime issues

### Which packages are impacted by your issue?

@graphql-codegen/typescript-rtk-query

### Describe the bug

In `packages/plugins/typescript/rtk-query/src/visitor.ts` in https://github.com/dotansimha/graphql-code-generator-community/commit/bebe34b2d141161d77348e85dbd223f04cba96e8 when the `TypedDocumentString` was introduced, the visitor was updated to output `document: ${documentVariableName} as unknown as string` - but at runtime `documentVariableName` is actually of type `TypedDocumentString`. This causes runtime issues as consuming code is expecting an actual string.

Proposed bugfix in https://github.com/jamesgecargo/graphql-code-generator-community/commit/5d02bf3ff30ffe13c7d0e8d3b182143cae8b50ac

### Your Example Website or App

https://github.com/jamesgecargo/graphql-code-generator-community/commit/5d02bf3ff30ffe13c7d0e8d3b182143cae8b50ac

### Steps to Reproduce the Bug or Issue

1. Regenerate any query
2. See the cast `as unknown as string`
3. Get runtime exception because a `TypedDocumentString` is getting passed around instead of an actual string

### Expected behavior

No runtime exceptions because the query should be a string, not a `TypedDocumentString`.

### Screenshots or Videos

_No response_

### Platform

- OS: Windows 11
- NodeJS: 24.11.0
- "graphql": "^16.13.2",
"graphql-request": "^6.1.0",
"@graphql-codegen/cli": "^7.2.0",
"@graphql-codegen/near-operation-file-preset": "^5.2.1",
"@graphql-codegen/typescript": "^6.1.0",
"@graphql-codegen/typescript-operations": "^6.1.0",
"@graphql-codegen/typescript-rtk-query": "^4.0.4",

### Codegen Config File

_No response_

### Additional context

_No response_

Start in packages/plugins/typescript/rtk-query/src/visitor.ts and inspect the generated document expression, then compare it with the proposed fix commit. Regenerate a query and verify that the emitted document is an actual string and no runtime exception occurs.

Written by the indexing model from the issue text.