test(e2e): point the Nova Sonic realtime test at nova-2-sonic

AWS retired amazon.nova-sonic-v1:0. GetFoundationModel now answers
ResourceNotFoundException "This model version has reached the end of its life",
and opening a bidirectional stream against it fails with ValidationException
"The provided model identifier is invalid". amazon.nova-2-sonic-v1:0 is the
active replacement.

The test passed on builds 219 (2026-09-16) and 246 (2026-09-17) and has failed
every run since, three attempts per build, with no litellm change to the
realtime path in between. The symptom was a clean websocket close: Bedrock ends
the stream rather than erroring, the forwarder treats a None receive as a normal
stream end and closes the client socket, so the client sees ConnectionClosedOK
and the test fails waiting for response.done.

litellm already carries both models in the cost map, with
"deprecation_date": "2026-09-14" on the old one, and the promptStart
transformation already sends the audioOutputConfiguration that nova-2-sonic
requires; only the test constant was left behind.

Verified against live Bedrock with the promptStart shape the transformation
builds: amazon.nova-sonic-v1:0 raises "The provided model identifier is
invalid", amazon.nova-2-sonic-v1:0 opens a session and returns a usageEvent.

The mocked handler and provider-cache tests keep the old id: it is only a label
there, no call reaches AWS.

tests/e2e/llm_translation/realtime/test_realtime_bedrock_e2e.py

@@ -25,7 +25,7 @@ from realtime_client import (
 
 pytestmark = pytest.mark.e2e
 
-NOVA_SONIC = "bedrock/amazon.nova-sonic-v1:0"
+NOVA_SONIC = "bedrock/amazon.nova-2-sonic-v1:0"
 
 
 class TestNovaSonicRealtime: