Update docker.io/postgres Docker tag to v18

.gitea/workflows/lint-test-helm.yaml

@@ -80,7 +80,7 @@ jobs:
             echo "$GIT_DIFF"
 
             for path in $GIT_DIFF; do
-              if [ echo "$path" | grep -q -E "clusters/[^/]+/helm/[^/]+" ]; then
+              if [[ echo "$path" | grep -q -E "clusters/[^/]+/helm/[^/]+" ]]; then
                 echo ""
                 echo ">> Adding path: $path"
                 CHANGED_CHARTS+=$(echo "$path" | awk -F '/' '{print $4}')