Upgrade Dockerfile to Go 1.18 (#3845)

* upgrade Dockerfile to go 1.18

* add blank line

* fix PiperGoUtils.groovy

DEVELOPMENT.md

@@ -29,6 +29,8 @@ First you need to set up an appropriate development environment:
 1. Install Go, see [GO Getting Started](https://golang.org/doc/install)
 1. Install an IDE with Go plugins, see for example [Go in Visual Studio Code](https://code.visualstudio.com/docs/languages/go)
 
+**Note:** The Go version to be used is the one specified in the "go.mod" file.
+
 ### Go basics
 
 In order to get yourself started, there is a lot of useful information out there.

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.17 AS build-env
+FROM golang:1.18 AS build-env
 COPY . /build
 WORKDIR /build
 

src/com/sap/piper/PiperGoUtils.groovy

@@ -25,7 +25,7 @@ class PiperGoUtils implements Serializable {
 
         if (steps.env.REPOSITORY_UNDER_TEST && steps.env.LIBRARY_VERSION_UNDER_TEST) {
             steps.echo("Running in a consumer test, building unit-under-test binary for verification.")
-            steps.dockerExecute(script: steps, dockerImage: 'golang:1.17', dockerOptions: '-u 0', dockerEnvVars: [
+            steps.dockerExecute(script: steps, dockerImage: 'golang:1.18', dockerOptions: '-u 0', dockerEnvVars: [
                 REPOSITORY_UNDER_TEST: steps.env.REPOSITORY_UNDER_TEST,
                 LIBRARY_VERSION_UNDER_TEST: steps.env.LIBRARY_VERSION_UNDER_TEST
             ]) {