test-gpu should be a skip-label

Author: brianseeders

.buildkite/pipelines/pull-request/.defaults.yml

@@ -1,5 +1,7 @@
 config:
-  skip-labels: ">test-mute"
+  skip-labels:
+    - ">test-mute"
+    - test-gpu # TODO remove this once the non-gpu steps work correctly
   excluded-regions:
     - ^docs/.*
     - ^x-pack/docs/.*