Add missing getAuthHeaders method to ClientContextStub

Fix TypeScript compilation error by implementing getAuthHeaders
method required by IClientContext interface.

Author: samikshya-db

tests/unit/.stubs/ClientContextStub.ts

@@ -1,3 +1,4 @@
+import { HeadersInit } from 'node-fetch';
 import IClientContext, { ClientConfig } from '../../../lib/contracts/IClientContext';
 import IConnectionProvider from '../../../lib/connection/contracts/IConnectionProvider';
 import IDriver from '../../../lib/contracts/IDriver';
@@ -48,4 +49,8 @@ export default class ClientContextStub implements IClientContext {
   public async getDriver(): Promise<IDriver> {
     return this.driver;
   }
+
+  public async getAuthHeaders(): Promise<HeadersInit> {
+    return {};
+  }
 }