Run gopls modernize on codebase (#34751)

Recent modernize fixes:
https://github.com/golang/tools/commits/master/gopls/internal/analysis/modernize

modules/charset/charset_test.go

@@ -242,7 +242,7 @@ func stringMustEndWith(t *testing.T, expected, value string) {
 func TestToUTF8WithFallbackReader(t *testing.T) {
 	resetDefaultCharsetsOrder()
 
-	for testLen := 0; testLen < 2048; testLen++ {
+	for testLen := range 2048 {
 		pattern := "    test { () }\n"
 		input := ""
 		for len(input) < testLen {