Fix RTE block rendering failing (#15583)

Adds optional class attribute to regex responsible for parsing RTE values to block models

Author: skttl

src/Umbraco.Infrastructure/PropertyEditors/ValueConverters/RichTextParsingRegexes.cs

@@ -4,6 +4,6 @@ namespace Umbraco.Cms.Core.PropertyEditors.ValueConverters;
 
 internal static partial class RichTextParsingRegexes
 {
-    [GeneratedRegex("<umb-rte-block(?:-inline)? data-content-udi=\"(?<udi>.[^\"]*)\"><!--Umbraco-Block--><\\/umb-rte-block(?:-inline)?>")]
+    [GeneratedRegex("<umb-rte-block(?:-inline)?(?: class=\"(.[^\"]*)\")? data-content-udi=\"(?<udi>.[^\"]*)\"><!--Umbraco-Block--><\\/umb-rte-block(?:-inline)?>")]
     public static partial Regex BlockRegex();
 }