Make bcr_compatibility less prone to bazel version change (#2119)

Avoid
https://buildkite.com/bazel/bcr-bazel-compatibility-test/builds/65#019361b1-b4ba-4e64-a78c-f8f4c54e54c6
diff --git a/buildkite/bazel-central-registry/bcr_compatibility.py b/buildkite/bazel-central-registry/bcr_compatibility.py
index f427d37..bb5608a 100644
--- a/buildkite/bazel-central-registry/bcr_compatibility.py
+++ b/buildkite/bazel-central-registry/bcr_compatibility.py
@@ -67,8 +67,12 @@
 
     top_n = os.environ.get('SELECT_TOP_BCR_MODULES')
     if top_n:
+        # Remove USE_BAZEL_VERSION to make this step more stable.
+        env = os.environ.copy()
+        env.pop("USE_BAZEL_VERSION", None)
         output = subprocess.check_output(
             ["bazel", "run", "//tools:module_analyzer", "--", "--name-only", f"--top_n={top_n}"],
+            env = env,
         )
         top_modules = output.decode("utf-8").split()
         MODULE_SELECTIONS = ','.join([f"{module}@latest" for module in top_modules])