test: adapt datumGateway jose test to v6 API

jose v6 removes the KeyLike type; keys are now Web Crypto CryptoKey.
Update the auth module test's key type annotation accordingly. The
runtime provider uses only APIs retained in v6 (createRemoteJWKSet,
jwtVerify) and needs no change.

Claude-Session: https://claude.ai/code/session_01NMSkwUcaTmZr7S5XmV2aFG

Author: scotwells

packages/backend/src/modules/authModuleDatumGatewayProvider.test.ts

@@ -13,7 +13,7 @@ const AUDIENCE = 'test-client-id.apps.googleusercontent.com';
 const HEADER = 'x-auth-request-id-token';
 const KID = 'test-key';
 
-let privateKey: jose.KeyLike;
+let privateKey: CryptoKey;
 
 const reqWith = (token?: string): Request =>
   ({