net: eliminate bounds checks in hasUpperCase

Function hasUpperCase accesses its parameter's bytes while iterating over
its runes. This approach muddles intent and causes an unnecessary bounds
check.

This CL makes hasUpperCase iterate over its parameter's bytes instead.

Updates #76354

Author: jub0bs

src/net/parse.go

@@ -182,8 +182,8 @@ func xtoi2(s string, e byte) (byte, bool) {
 
 // hasUpperCase tells whether the given string contains at least one upper-case.
 func hasUpperCase(s string) bool {
-	for i := range s {
-		if 'A' <= s[i] && s[i] <= 'Z' {
+	for _, b := range []byte(s) {
+		if 'A' <= b && b <= 'Z' {
 			return true
 		}
 	}