[tune] add data to CI test dependencies (#33729)

1. #33565 introduced  `DATA_PROCESSING_TESTING=1` as a requirement to  `:octopus: Tune tests and examples (medium)"`.
2. #33609 introduced `":octopus: :spiral_note_pad: New output: Tune tests and examples (medium)"` as a copy of `:octopus: Tune tests and examples (medium)"` but was done prior to merging (1).
3. #33499 introduced a `":octopus: :sunny: New execution path:Tune tests and examples (medium)"` as a copy of `:octopus: Tune tests and examples (medium)"` but was done prior to merging (1).

**Note:** There should probably be a better way for handling dependencies in CI tests...

.buildkite/pipeline.ml.yml

@@ -289,7 +289,7 @@
   instance_size: medium
   commands:
     - cleanup() { if [ "${BUILDKITE_PULL_REQUEST}" = "false" ]; then ./ci/build/upload_build_info.sh; fi }; trap cleanup EXIT
-    - TUNE_TESTING=1 ./ci/env/install-dependencies.sh
+    - TUNE_TESTING=1 DATA_PROCESSING_TESTING=1 ./ci/env/install-dependencies.sh
     - ./ci/env/env_info.sh
     - bazel test --config=ci $(./ci/run/bazel_export_options) --build_tests_only
       --test_tag_filters=medium_instance,-py37,-soft_imports,-gpu_only,-rllib,-multinode
@@ -348,7 +348,7 @@
   instance_size: medium
   commands:
     - cleanup() { if [ "${BUILDKITE_PULL_REQUEST}" = "false" ]; then ./ci/build/upload_build_info.sh; fi }; trap cleanup EXIT
-    - TUNE_TESTING=1 ./ci/env/install-dependencies.sh
+    - TUNE_TESTING=1 DATA_PROCESSING_TESTING=1 ./ci/env/install-dependencies.sh
     - ./ci/env/env_info.sh
     - bazel test --config=ci $(./ci/run/bazel_export_options) --build_tests_only
       --test_env=TUNE_NEW_EXECUTION=1