chore: fix missing \n at end of exported patches (#15579) (#15619)

(cherry picked from commit 2e1c50c891e31e9a949c370683a77ee705a162f6)

script/git-export-patches

@@ -123,7 +123,7 @@ def main(argv):
     for patch in patches:
       filename = get_file_name(patch)
       with open(os.path.join(out_dir, filename), 'w') as f:
-        f.write('\n'.join(remove_patch_filename(patch)))
+        f.write('\n'.join(remove_patch_filename(patch)).rstrip('\n') + '\n')
       pl.write(filename + '\n')