Fix removing MODULE.bazel file (#2154)

Addressing
https://github.com/bazelbuild/bazel-central-registry/pull/3538#issuecomment-2575643477
diff --git a/buildkite/bazel-central-registry/bcr_presubmit.py b/buildkite/bazel-central-registry/bcr_presubmit.py
index 6119f80..21040d6 100755
--- a/buildkite/bazel-central-registry/bcr_presubmit.py
+++ b/buildkite/bazel-central-registry/bcr_presubmit.py
@@ -28,6 +28,7 @@
 import sys
 import subprocess
 import shutil
+import stat
 import time
 import urllib.request
 import zipfile
@@ -251,6 +252,7 @@
     module_dot_bazel = source_root.joinpath("MODULE.bazel")
     # In case the existing MODULE.bazel has no write permission.
     if module_dot_bazel.exists():
+        os.chmod(module_dot_bazel, stat.S_IWRITE)
         os.remove(module_dot_bazel)
     shutil.copy(checked_in_module_dot_bazel, module_dot_bazel)