fix: docker/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

Author: snyk-bot

docker/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.18 as builder
+FROM alpine:3 as builder
 
 WORKDIR /workdir
 
@@ -26,7 +26,7 @@ RUN cargo fetch
 
 RUN cargo build --features freeze-stdlib --release --locked --offline --bin rustpython
 
-FROM alpine:3.18
+FROM alpine:3
 
 RUN apk --no-cache add musl libgcc