fix(test): align proxy-exception test assertion with humanized error wording

The rebase onto main pulled in the humanized auth error messages
(97dbe29) which changed "wasn't recognized" to "I don't recognize
this key". Update the non-chat client test assertion to match.

Author: SebConejo

packages/backend/src/routing/proxy/__tests__/proxy-exception.filter.spec.ts

@@ -203,7 +203,7 @@ describe('ProxyExceptionFilter', () => {
           error: expect.objectContaining({
             type: 'auth_error',
             code: 'manifest_auth',
-            message: expect.stringContaining("wasn't recognized"),
+            message: expect.stringContaining("don't recognize this key"),
           }),
         }),
       );