testing/blackbox_exporter: add missing exit 0

testing/blackbox_exporter/APKBUILD

 # Maintainer: ungleich <alpinelinux@ungleich.ch>
 pkgname=blackbox_exporter
 pkgver=0.19.0
-pkgrel=0
+pkgrel=1
 pkgdesc="Prometheus Blackbox Exporter"
 url="https://github.com/prometheus/blackbox_exporter"
 license="Apache-2.0"

testing/blackbox_exporter/blackbox_exporter.pre-install

@@ -2,3 +2,4 @@
 addgroup -S prometheus 2>/dev/null
 adduser -SDh/var/lib/prometheus \
 	-s/sbin/nologin -Gprometheus -gprometheus prometheus prometheus 2>/dev/null
+exit 0