Move python/BUILD to python/BUILD.bazel

This should address the issue in #14600 by avoiding a conflict on with the
`build` directory created by setup.py on a case-insensitive filesystem.

Closes #14600.

PiperOrigin-RevId: 579859556

python/build_targets.bzl

diff --git a/python/build_targets.bzl b/python/build_targets.bzl
index 91c8dfb..fff32b4 100644
--- a/python/build_targets.bzl
+++ b/python/build_targets.bzl
@@ -456,7 +456,7 @@
             "google/protobuf/pyext/*.cc",
             "google/protobuf/pyext/*.h",
         ]) + [
-            "BUILD",
+            "BUILD.bazel",
             "MANIFEST.in",
             "README.md",
             "build_targets.bzl",