fix: Dockerfile to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-ALPINE322-BUSYBOX-14091698
- https://snyk.io/vuln/SNYK-ALPINE322-BUSYBOX-14091698
- https://snyk.io/vuln/SNYK-ALPINE322-BUSYBOX-14091698
- https://snyk.io/vuln/SNYK-ALPINE322-BUSYBOX-14091701
- https://snyk.io/vuln/SNYK-ALPINE322-BUSYBOX-14091701

Dockerfile

@@ -17,7 +17,7 @@ fi
 /go/build.sh ${ARGS}
 __SCRIPT__
 
-FROM alpine:3.23.3
+FROM alpine:3.23.2
 ARG TARGETOS
 ARG TARGETARCH
 ARG TARGETVARIANT

assets/start-psiphon

@@ -19,9 +19,6 @@ if [ ! -f /config/psiphon.config ]; then
     if [ -n "${EGRESS_REGION}" ]; then
         sed -i -E 's/"EgressRegion"[[:space:]]*:[[:space:]]*"[^"]*"/"EgressRegion": "'${EGRESS_REGION}'"/' /config/psiphon.config
     fi
-    if [ -n "${UPSTREAM_PROXY}" ]; then
-        sed -i -E 's|"UpstreamProxyUrl"[[:space:]]*:[[:space:]]*"[^"]*"|"UpstreamProxyUrl": "'${UPSTREAM_PROXY}'"|' /config/psiphon.config
-    fi
 fi
 
 id psiphon > /dev/null 2>&1
@@ -46,4 +43,4 @@ chown -R psiphon:psiphon /config
 
 su -s /bin/sh psiphon <<EOF
 psiphon -config /config/psiphon.config
-EOF
+EOF