Fix regeneration of RegistrationTestData.assertion

This was broken in commit 8474644 because the
`copy` method is no longer used, so `this.assertion` is no longer copied into
`newValue`, and therefore `newValue.assertion` is always `None` in this `.map`
call. The fix is to call `.map` on `this.assertion` (which is still the old
value, which may be `Some`) instead of on `newValue.assertion` (which is always
`None`).

Author: emlun

webauthn-server-core/src/test/scala/com/yubico/webauthn/RegistrationTestData.scala

@@ -911,7 +911,7 @@ case class RegistrationTestData(
       val newValue =
         RegistrationTestData.from(credential, keypair, attestationCertChain)
       newValue.copy(
-        assertion = newValue.assertion.map(_.regenerate(newValue))
+        assertion = assertion.map(_.regenerate(newValue))
       )
     })