Update koalaman/shellcheck-alpine Docker tag to v0.9.0

Reviewed-on: coop-cloud/abra-hetzner#1

.drone.yml

@@ -3,7 +3,7 @@ kind: pipeline
 name: linters
 steps:
   - name: run shellcheck
-    image: koalaman/shellcheck-alpine:v0.7.1
+    image: koalaman/shellcheck-alpine:v0.9.0
     commands:
       - shellcheck abra-hetzner
 trigger:

renovate.json

@@ -0,0 +1,3 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json"
+}