[core] Don't trigger Spark-on-Ray tests with java tag (#57993)

Although Spark-on-Ray depends on the Java bindings, we `java` tests are
triggered by all C++ changes and we don't want to run Spark-on-Ray tests
every time we change C++ code.

---------

Signed-off-by: Edward Oakes <ed.nmi.oakes@gmail.com>

Author: edoakes

.buildkite/core.rayci.yml

@@ -451,9 +451,10 @@ steps:
       - corebuild
 
   - label: ":core: core: spark-on-ray tests"
+    # NOTE: The Spark-on-Ray tests intentionally aren't triggered by the `java` tag to
+    # avoid running them for every C++ code change.
     tags:
       - spark_on_ray
-      - java
       - oss
     instance_type: medium
     commands: