Fix task-list checkbox styling (#10668)

* Fix task-list checkbox styling

The pandoc renderer will append the class "task-list" to the ul element
wrapping a li with one or more check-boxes. This allows us to select for
them, removing their list-style-type property. However, goldmark and the
gfm spec doesn't specify the "task-list" class name, so we can't use
that to fix the issue there.

Signed-off-by: Alexander Scheel <alexander.m.scheel@gmail.com>

* Update to goldmark v1.1.25

This version adds the missing space after a checkbox.

Resolves: #9656

Signed-off-by: Alexander Scheel <alexander.m.scheel@gmail.com>

Co-authored-by: zeripath <art27@cantab.net>

modules/markup/sanitizer.go

@@ -53,6 +53,9 @@ func ReplaceSanitizer() {
 	// Allow classes for anchors
 	sanitizer.policy.AllowAttrs("class").Matching(regexp.MustCompile(`ref-issue`)).OnElements("a")
 
+	// Allow classes for task lists
+	sanitizer.policy.AllowAttrs("class").Matching(regexp.MustCompile(`task-list`)).OnElements("ul")
+
 	// Allow generally safe attributes
 	generalSafeAttrs := []string{"abbr", "accept", "accept-charset",
 		"accesskey", "action", "align", "alt",