use go1.18 to build gitea (#19099)

* use go1.18 to build gitea& update min go version to 1.17

* bump in a few more places

* add a few simple tests for isipprivate

* update go.mod

* update URL to https://go.dev/dl/

* golangci-lint

* attempt golangci-lint workaround

* change version

* bump fumpt version

* skip strings.title test

* go mod tidy

* update tests as some aren't private??

* update tests

Dockerfile.rootless

@@ -1,5 +1,5 @@
 #Build stage
-FROM golang:1.17-alpine3.15 AS build-env
+FROM golang:1.18-alpine3.15 AS build-env
 
 ARG GOPROXY
 ENV GOPROXY ${GOPROXY:-direct}