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/chasquid-util/chasquid-util.go

@@ -1,6 +1,7 @@
 // chasquid-util is a command-line utility for chasquid-related operations.
 //
 // Don't include it in the coverage build.
+//go:build !coverage
 // +build !coverage
 
 package main

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

cmd/mda-lmtp/mda-lmtp.go

@@ -2,6 +2,7 @@
 //
 // See the usage below for details.
 //
+//go:build !coverage
 // +build !coverage
 
 package main

cmd/smtp-check/smtp-check.go

@@ -1,5 +1,6 @@
 // smtp-check is a command-line too for checking SMTP setups.
 //
+//go:build !coverage
 // +build !coverage
 
 package main

cmd/spf-check/spf-check.go

@@ -1,6 +1,7 @@
 // Command line tool for playing with the SPF library.
 //
 // Not for use in production, just development and experimentation.
+//go:build !coverage
 // +build !coverage
 
 package main