Issue #241 - fix deferred authentication for Java21 EE10 runtime

[lachlan-roberts]

closes #241

If request.getUserPrincipal() was being called on a request with deferred authentication, then authentication was failing.

This is because the isDeferred check in EE10AppEngineAuthentication was in the wrong place.

[ludoch]

Code fix is now checked in.
Will reach prod end of next week or next (due to 4rth of July break in US).
Meanwhile, you can try following for the next few days https://github.com/GoogleCloudPlatform/appengine-java-standard/blob/main/TRYLATESTBITSINPROD.md from head (Sorry, Maven only, gradle contribution welcome).