[libxml2] Also build CI tests with -Werror

[Nick Wellnhofer <nwellnhof src gnome org>]

commit dbc23ed301ba7270ebb3e8735a17f96ce15fdc4c
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Wed Apr 13 17:02:50 2022 +0200

    Also build CI tests with -Werror

 .gitlab-ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 2e079f68..f3ac54d5 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -21,7 +21,7 @@
       ln -s /tests/xmlconf
       sh autogen.sh $CONFIG
       make -j$(nproc) V=1 CFLAGS="$CFLAGS -Werror"
-      make check
+      make CFLAGS="$CFLAGS -Werror" check
 
 gcc:
   extends: .test