test: replace `// +build` syntax with `//go:build`

PR #955 removed the use of the // +build syntax, which has been deprecated since Go version 1.18.

However, the tests in the test/compare directory have been maintained as they are because the parsing of test directives, which occurs here:

scriggo/test/compare/run.go

Lines 160 to 168 in 527b6c2

    
           if !imports.ShouldBuild(src, tags) { 
        
           	atomic.AddInt64(&countIncompatible, 1) 
        
           	if *verbose { 
        
           		fmt.Println("[ skipped, not compatible ]") 
        
           	} 
        
           	<-queue 
        
           	wg.Done() 
        
           	return 
        
           }

uses the package:

https://pkg.go.dev/github.com/rogpeppe/go-internal@v1.13.1/imports

whose function ShouldBuild still only supports the old format of build tags:

https://pkg.go.dev/github.com/rogpeppe/go-internal@v1.13.1/imports#ShouldBuild

So, it is a matter of finding an alternative way to parse the lines containing build directives in the tests. Until then, we will maintain the old directive format in the tests.

	if !imports.ShouldBuild(src, tags) {
	atomic.AddInt64(&countIncompatible, 1)
	if *verbose {
	fmt.Println("[ skipped, not compatible ]")
	}
	<-queue
	wg.Done()
	return
	}