cmd/go: add newline after module-requires-version message

Fixes #30263

Change-Id: Iefb3d8baf815c19eaf915a59048e1da799ca0cdf
Reviewed-on: https://go-review.googlesource.com/c/162957
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

src/cmd/go/internal/work/exec.go

@@ -655,7 +655,7 @@ func (b *Builder) build(a *Action) (err error) {
 	if len(out) > 0 {
 		output := b.processOutput(out)
 		if p.Module != nil && !allowedVersion(p.Module.GoVersion) {
-			output += "note: module requires Go " + p.Module.GoVersion
+			output += "note: module requires Go " + p.Module.GoVersion + "\n"
 		}
 		b.showOutput(a, a.Package.Dir, a.Package.Desc(), output)
 		if err != nil {