fix: client/Dockerfile to reduce vulnerabilities (#3019)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE320-OPENSSL-8235201
- https://snyk.io/vuln/SNYK-ALPINE320-OPENSSL-8235201

Co-authored-by: snyk-bot <snyk-bot@snyk.io>

client/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.20
+FROM alpine:3.21.0
 RUN apk add --no-cache ca-certificates iptables ip6tables
 ENV NB_FOREGROUND_MODE=true
 ENTRYPOINT [ "/usr/local/bin/netbird","up"]