tests/pull-sizes: Disable xattrs everywhere

I am getting SELinux xattrs committed in local development (inside
https://github.com/cgwalters/coretoolbox ), which
throws off the hardcoded sizes in this test.

tests/test-pull-sizes.sh

@@ -23,6 +23,8 @@ set -euo pipefail
 
 . $(dirname $0)/libtest.sh
 
+# Committing SELinux attributes throws off the hardcoded sizes below
+export OSTREE_NO_XATTRS=1
 setup_fake_remote_repo1 "archive" "--generate-sizes"
 
 echo '1..3'