CI: editor-config: adjust for 'pmbootstrap ci' (MR 3615)

.ci/ec.sh

+#!/bin/sh -e
+# Description: editorconfig-checker: lint for trailing whitespaces etc.
+# https://postmarktos.org/pmb-ci
+
+if [ "$(id -u)" = 0 ]; then
+	set -x
+	apk -q add \
+		editorconfig-checker
+	exec su "${TESTUSER:-build}" -c "sh -e $0"
+fi
+
+set -x
+ec

.gitlab-ci.yml

@@ -65,10 +65,9 @@ editor-config:
   stage: lint
   <<: *only-default
   image: alpine:edge
-  before_script:
-    - apk -q add editorconfig-checker
   script:
-    - ec
+    - .ci/lib/gitlab_prepare_ci.sh
+    - .ci/ec.sh
 
 # aports checks (generic)
 aports-static: