`createFromGoogleCredential` is not compatible with `google-auth-library` 10.x.x

### Problem description
`google-auth-library` 10.x adopted and moved forward to node native fetch. Thus they switched from
```ts
export interface Headers {
[index: string]: string;
}
```
to Headers defined in Node.

`createFromGoogleCredential` uses the following interface

```ts
export interface CurrentOAuth2Client {
getRequestHeaders: (url?: string) => Promise<{
[index: string]: string;
}>;
}
```
which is incompatible.

### Reproduction steps
Try `createFromGoogleCredential` with a client created with google-auth-library 10.x

### Environment
- OS name, version and architecture: aarch64, MacOS
- Node version: 21
- Node installation method: volta
- If applicable, compiler version [e.g. clang 3.8.0-2ubuntu4]
- Package name and version "@grpc/grpc-js": "^1.13.0",

### Additional context