Stage the Python license file during builds (#9015)

Copy the repo-root LICENSE into the Python package directory for the duration of setup() so license_files = LICENSE remains valid without using deprecated parent-directory paths.

Remove the staged copy after the build completes.

python/setup.py

@@ -12,8 +12,26 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from pathlib import Path
+import shutil
+
 from setuptools import setup
 
+
+_THIS_DIR = Path(__file__).resolve().parent
+_ROOT_LICENSE = _THIS_DIR.parent / 'LICENSE'
+_LOCAL_LICENSE = _THIS_DIR / 'LICENSE'
+
+
+def _stage_license_file():
+    if _LOCAL_LICENSE.exists() or not _ROOT_LICENSE.exists():
+        return False
+    shutil.copyfile(_ROOT_LICENSE, _LOCAL_LICENSE)
+    return True
+
+_remove_staged_license = _stage_license_file()
+
+try:
     setup(
         name='flatbuffers',
         version='25.12.19',
@@ -42,3 +60,6 @@ setup(
             'Source': 'https://github.com/google/flatbuffers',
         },
     )
+finally:
+    if _remove_staged_license and _LOCAL_LICENSE.exists():
+        _LOCAL_LICENSE.unlink()