Fix lint warnings (#4586)

go run golang.org/x/tools/gopls/internal/analysis/modernize/cmd/modernize@latest -fix -test ./...

src/util/atexit_test.go

@@ -8,7 +8,7 @@ import (
 func TestAtExit(t *testing.T) {
 	want := []int{3, 2, 1, 0}
 	var called []int
-	for i := 0; i < 4; i++ {
+	for i := range 4 {
 		n := i
 		AtExit(func() { called = append(called, n) })
 	}

src/util/chars.go

@@ -52,7 +52,7 @@ func ToChars(bytes []byte) Chars {
 	}
 
 	runes := make([]rune, bytesUntil, len(bytes))
-	for i := 0; i < bytesUntil; i++ {
+	for i := range bytesUntil {
 		runes[i] = rune(bytes[i])
 	}
 	for i := bytesUntil; i < len(bytes); {
@@ -259,7 +259,7 @@ func (chars *Chars) Lines(multiLine bool, maxLines int, wrapCols int, wrapSignWi
 		lines = append(lines, text)
 	} else {
 		from := 0
-		for off := 0; off < len(text); off++ {
+		for off := range text {
 			if text[off] == '\n' {
 				lines = append(lines, text[from:off+1]) // Include '\n'
 				from = off + 1