chore: use strings.Contains and bytes.Contains instead

pkg/webdav/internal/xml/marshal.go

@@ -1042,14 +1042,14 @@ func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
 			switch k {
 			case reflect.String:
 				s := vf.String()
-				dashDash = strings.Index(s, "--") >= 0
+				dashDash = strings.Contains(s, "--")
 				dashLast = s[len(s)-1] == '-'
 				if !dashDash {
 					p.WriteString(s)
 				}
 			case reflect.Slice:
 				b := vf.Bytes()
-				dashDash = bytes.Index(b, ddBytes) >= 0
+				dashDash = bytes.Contains(b, ddBytes)
 				dashLast = b[len(b)-1] == '-'
 				if !dashDash {
 					p.Write(b)