junit: Specify unicode replacement character as \uFFFD

This is just to make the exact character we want to return explicit,
otherwise it could be confused by any unsupported character in your text
editor.

junit/junit.go

@@ -244,14 +244,14 @@ func escapeIllegalChars(str string) string {
 		if isInCharacterRange(r) {
 			return r
 		}
-		return '<EFBFBD>'
+		return '\uFFFD'
 	}, str)
 }
 
 // Decide whether the given rune is in the XML Character Range, per
 // the Char production of https://www.xml.com/axml/testaxml.htm,
 // Section 2.2 Characters.
-// Form: encoding/xml/xml.go
+// From: encoding/xml/xml.go
 func isInCharacterRange(r rune) (inrange bool) {
 	return r == 0x09 ||
 		r == 0x0A ||