Add a simple test for external renderer (#20033)

Fix #16402

tests/gitea-repositories-meta/user30/renderer.git/hooks/post-receive

@@ -0,0 +1,15 @@
+#!/usr/bin/env bash
+data=$(cat)
+exitcodes=""
+hookname=$(basename $0)
+GIT_DIR=${GIT_DIR:-$(dirname $0)}
+
+for hook in ${GIT_DIR}/hooks/${hookname}.d/*; do
+test -x "${hook}" && test -f "${hook}" || continue
+echo "${data}" | "${hook}"
+exitcodes="${exitcodes} $?"
+done
+
+for i in ${exitcodes}; do
+[ ${i} -eq 0 ] || exit ${i}
+done