build: revert gnulib update

There is a pending issue with fchownat:
https://lists.gnu.org/r/bug-gnulib/2025-09/msg00282.html

diff --git a/gnulib b/gnulib
index d947a2d927b95f33cc35eee0b96d7b46dfc81ecb..9d7a6e011389cd02c91194e82d105e0a9698dfbe 160000 (submodule)
--- a/gnulib
+++ b/gnulib
@@ -1 +1 @@
-Subproject commit d947a2d927b95f33cc35eee0b96d7b46dfc81ecb
+Subproject commit 9d7a6e011389cd02c91194e82d105e0a9698dfbe