markup/goldmark: Adjust auto ID space handling

GitHub does not consider tabs as delimiter, see https://github.com/bep/portable-hugo-links/blob/master/blog/p2.md

Closes #6710

markup/goldmark/autoid.go

@@ -58,7 +58,7 @@ func sanitizeAnchorNameWithHook(b []byte, idType string, hook func(buf *bytes.Bu
 			r, size := utf8.DecodeRune(b)
 			switch {
 			case asciiOnly && size != 1:
-			case r == '-' || isSpace(r):
+			case r == '-' || r == ' ':
 				buf.WriteRune('-')
 			case isAlphaNumeric(r):
 				buf.WriteRune(unicode.ToLower(r))
@@ -85,10 +85,6 @@ func isAlphaNumeric(r rune) bool {
 	return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
 }
 
-func isSpace(r rune) bool {
-	return r == ' ' || r == '\t'
-}
-
 var _ parser.IDs = (*idFactory)(nil)
 
 type idFactory struct {

markup/goldmark/autoid_test.go

@@ -40,6 +40,8 @@ Many   spaces  here
 Forward/slash
 Backward\slash
 Under_score
+Nonbreaking Space
+Tab	Space
 `
 
 	expect := `
@@ -56,6 +58,8 @@ many---spaces--here
 forwardslash
 backwardslash
 under_score
+nonbreakingspace
+tabspace
 `
 
 	tests, expect = strings.TrimSpace(tests), strings.TrimSpace(expect)