Update build tag constraints

This patch updates all build tag constraints to add the new format,
alongside the old one, to maintain backwards compatibility.

This was done by using `go fmt`.

See https://go.dev/doc/go1.17#gofmt and
https://golang.org/design/draft-gobuild for more details.

test/util/conngen.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 // SMTP connection generator, for testing purposes.

test/util/coverhtml.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 // Generate an HTML visualization of a Go coverage profile.

test/util/fexp.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 // Fetch an URL, and check if the response matches what we expect.

test/util/generate_cert.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build ignore
 // +build ignore
 
 // Generate a self-signed X.509 certificate for a TLS server. Outputs to

test/util/gocovcat.go

@@ -2,6 +2,7 @@
 //
 // From: https://git.lukeshu.com/go/cmd/gocovcat/
 //
+//go:build ignore
 // +build ignore
 
 // Copyright 2017 Luke Shumaker <lukeshu@parabola.nu>

test/util/loadgen.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 // SMTP load generator, for testing purposes.

test/util/minidns.go

@@ -1,3 +1,4 @@
+//go:build ignore
 // +build ignore
 
 // minidns is a trivial DNS server used for testing.