fix: Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE318-OPENSSL-7413525
- https://snyk.io/vuln/SNYK-ALPINE318-OPENSSL-7413525
- https://snyk.io/vuln/SNYK-ALPINE318-OPENSSL-7413536
- https://snyk.io/vuln/SNYK-ALPINE318-OPENSSL-7413536

Dockerfile

@@ -47,7 +47,7 @@ RUN go install github.com/yaegashi/muslstack@latest && \
 
 # ---
 
-FROM alpine:3.18
+FROM alpine:3
 
 # renew global args from above & pin any dependency versions
 ARG HUGO_VERSION