contrib/packit-tmt: handle missing testing-farm repo

Check for testing-farm-tag-repository before passing --disable-repo to dnf.
This prevents the dependency upgrade from failing when Testing Farm did
not create the repository.

Fixes: #28452

Signed-off-by: rsvr76 <vishnuramrs07@gmail.com>

contrib/packit-tmt/update-deps.sh

@@ -2,6 +2,11 @@
 
 set -exo pipefail
 
+DISABLE_REPO=()
+if grep -s -r -q -F '[testing-farm-tag-repository]' /etc/yum.repos.d 2>/dev/null; then
+    DISABLE_REPO=(--disable-repo=testing-farm-tag-repository)
+fi
+
 # This should work even when podman-next isn't installed. It'll fetch the
 # highest versions available across all repos.
-dnf -y upgrade --allowerasing --disable-repo=testing-farm-tag-repository --exclude=podman*
+dnf -y upgrade --allowerasing "${DISABLE_REPO[@]}" --exclude=podman*