Also print --migrate annotations for regular pipelines (#837)

If a regular (=non-downstream) pipeline is run with the USE_BAZELISK_MIGRATE env var, this commit ensures that Buildkite displays annotations for all flags that must be migrated, similar to the current behavior in a downstream pipeline.
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index 43d5423..deeb46f 100755
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -1907,6 +1907,15 @@
     if "validate_config" in configs:
         pipeline_steps += create_config_validation_steps()
 
+    if use_bazelisk_migrate() and not is_downstream_project:
+        # Print results of bazelisk --migrate in project pipelines that explicitly set
+        # the USE_BAZELISK_MIGRATE env var, but that are not being run as part of a
+        # downstream pipeline.
+        number = os.getenv("BUILDKITE_BUILD_NUMBER")
+        pipeline_steps += get_steps_for_aggregating_migration_results(
+            number, script_org, script_branch
+        )
+
     print_pipeline_steps(pipeline_steps, handle_emergencies=not is_downstream_project)
 
 
@@ -2388,19 +2397,8 @@
         if not current_build_number:
             raise BuildkiteException("Not running inside Buildkite")
         if use_bazelisk_migrate():
-            pipeline_steps.append({"wait": "~", "continue_on_failure": "true"})
-            pipeline_steps.append(
-                create_step(
-                    label="Aggregate incompatible flags test result",
-                    commands=[
-                        fetch_bazelcipy_command(),
-                        fetch_aggregate_incompatible_flags_test_result_command(),
-                        PLATFORMS[DEFAULT_PLATFORM]["python"]
-                        + " aggregate_incompatible_flags_test_result.py --build_number=%s"
-                        % current_build_number,
-                    ],
-                    platform=DEFAULT_PLATFORM,
-                )
+            pipeline_steps += get_steps_for_aggregating_migration_results(
+                current_build_number
             )
         else:
             pipeline_steps.append({"wait": "~", "continue_on_failure": "true"})
@@ -2440,6 +2438,27 @@
     print_pipeline_steps(pipeline_steps)
 
 
+def get_steps_for_aggregating_migration_results(current_build_number):
+    parts = [
+        PLATFORMS[DEFAULT_PLATFORM]["python"],
+        "aggregate_incompatible_flags_test_result.py",
+        "--build_number=%s" % current_build_number,
+        "--pipeline=%s" % os.getenv("BUILDKITE_PIPELINE_SLUG"),
+    ]
+    return [
+        {"wait": "~", "continue_on_failure": "true"},
+        create_step(
+            label="Aggregate incompatible flags test result",
+            commands=[
+                fetch_bazelcipy_command(),
+                fetch_aggregate_incompatible_flags_test_result_command(),
+                " ".join(parts),
+            ],
+            platform=DEFAULT_PLATFORM,
+        ),
+    ]
+
+
 def bazelci_builds_download_url(platform, git_commit):
     bucket_name = "bazel-testing-builds" if THIS_IS_TESTING else "bazel-builds"
     return "https://storage.googleapis.com/{}/artifacts/{}/{}/bazel".format(