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.

cmd/dovecot-auth-cli/coverage_test.go

@@ -3,6 +3,7 @@
 //
 // See coverage_test.go for the details, this is the same horrible hack.
 //
+//go:build coveragebin
 // +build coveragebin
 
 package main