alpine 3.16 (#19797)

Co-authored-by: 6543 <6543@obermui.de>

Dockerfile

 #Build stage
-FROM golang:1.18-alpine3.15 AS build-env
+FROM golang:1.18-alpine3.16 AS build-env
 
 ARG GOPROXY
 ENV GOPROXY ${GOPROXY:-direct}
 # Begin env-to-ini build
 RUN go build contrib/environment-to-ini/environment-to-ini.go
 
-FROM alpine:3.15
+FROM alpine:3.16
 LABEL maintainer="maintainers@gitea.io"
 
 EXPOSE 22 3000

Dockerfile.rootless

 #Build stage
-FROM golang:1.18-alpine3.15 AS build-env
+FROM golang:1.18-alpine3.16 AS build-env
 
 ARG GOPROXY
 ENV GOPROXY ${GOPROXY:-direct}
 # Begin env-to-ini build
 RUN go build contrib/environment-to-ini/environment-to-ini.go
 
-FROM alpine:3.15
+FROM alpine:3.16
 LABEL maintainer="maintainers@gitea.io"
 
 EXPOSE 2222 3000