Docker Alpine: update to 3.18

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

Dockerfile.alpine

@@ -1,4 +1,4 @@
-FROM golang:1.20-alpine3.17 AS builder
+FROM golang:1.20-alpine3.18 AS builder
 
 ENV GOFLAGS="-mod=readonly"
 
@@ -27,7 +27,7 @@ RUN set -xe && \
 
 RUN apk add --update --no-cache openssh-client-common libcap && setcap cap_net_bind_service=+ep /workspace/sftpgo
 
-FROM alpine:3.17
+FROM alpine:3.18
 
 # Set to "true" to install jq and the optional git and rsync dependencies
 ARG INSTALL_OPTIONAL_PACKAGES=false