fix: docker/Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE315-OPENSSL-3314621
- https://snyk.io/vuln/SNYK-ALPINE315-OPENSSL-3314621
- https://snyk.io/vuln/SNYK-ALPINE315-OPENSSL-3314622
- https://snyk.io/vuln/SNYK-ALPINE315-OPENSSL-3314622
- https://snyk.io/vuln/SNYK-ALPINE315-ZLIB-2976173

docker/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.15.4
+FROM alpine:3.18.6
 
 RUN mkdir /www