Add back rules_python in downstream pipeline (#2105)

https://github.com/bazelbuild/continuous-integration/pull/2101#issuecomment-2460663209
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index afd19be..b408ea2 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -229,6 +229,10 @@
         "pipeline_slug": "rules-platform",
         "owned_by_bazel": True,
     },
+    "rules_python": {
+        "git_repository": "https://github.com/bazelbuild/rules_python.git",
+        "pipeline_slug": "rules-python-python",
+    },
     "rules_testing": {
         "git_repository": "https://github.com/bazelbuild/rules_testing.git",
         "pipeline_slug": "rules-testing",