fix: Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE318-BUSYBOX-7249236
- https://snyk.io/vuln/SNYK-ALPINE318-BUSYBOX-7249265
- https://snyk.io/vuln/SNYK-ALPINE318-BUSYBOX-7249265
- https://snyk.io/vuln/SNYK-ALPINE318-BUSYBOX-7249419
- https://snyk.io/vuln/SNYK-ALPINE318-BUSYBOX-7249419

Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.18
+FROM alpine:3
 ENV APP_USER=regula
 ENV APP_DIR=/workspace
 RUN adduser -s /bin/true -u 1000 -D -h $APP_DIR $APP_USER