Fix type error

[itsmeabhishek03]

Fixes #3506

This PR resolves TypeScript compilation errors caused by missing explicit types in the GetScreenCallback type definition in janus.d.ts.

Issue Details:
Problem: The GetScreenCallback type was defined as:

type GetScreenCallback = (error?, sourceId?) => void;
This caused TypeScript errors (TS7006) when compiling in strict mode, as the parameters error and sourceId implicitly had the any type.

Solution: The parameters have been updated with explicit types to ensure compatibility with strict TypeScript settings:
type GetScreenCallback = (error:string, sourceId:string) => void

[januscla]

Thanks for your contribution, @itsmeabhishek03! Please make sure you sign our CLA, as it's a required step before we can merge this.

[lminiero]

Thanks for spotting this and for the fix, @itsmeabhishek03, merging!