fix: docker/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE319-OPENSSL-7413523
- https://snyk.io/vuln/SNYK-ALPINE319-OPENSSL-7413523
- https://snyk.io/vuln/SNYK-ALPINE319-OPENSSL-7413527
- https://snyk.io/vuln/SNYK-ALPINE319-OPENSSL-7413527

Author: snyk-bot

docker/Dockerfile

@@ -1,5 +1,5 @@
 # syntax=docker/dockerfile:1
-FROM alpine:3.19
+FROM alpine:3
 
 ARG VERSION="1.2.6.7"
 ARG DIST_URL="https://github.com/leenooks/phpLDAPadmin/archive/refs/tags/${VERSION}.tar.gz"