Add job to ensure we support the default COS driver.

Add job to run GPU tests against COS's default driver.
COS doesn't have a way to nicely install and uninstall
driver versions, let alone have it work with how we run
tests on COS itself. Add a workflow that runs on VMs
that install the default driver instead of the latest.

PiperOrigin-RevId: 670700420

.buildkite/pipeline.yaml

@@ -184,6 +184,13 @@ steps:
       - make cos-gpu-all-tests
     agents:
       queue: cos-canary-gpu
+  - <<: *common
+    <<: *source_test_continuous
+    label: ":male_supervillain: COS GPU Tests (Default)"
+    commands:
+      - make cos-gpu-all-tests
+    agents:
+      queue: cos-canary-gpu-default
   - <<: *common
     <<: *source_test_continuous
     label: ":screwdriver: All GPU Drivers Test"