markdown: Ignore html comments (#28318)

Closes #28300

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| ------ | ----- |
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![Screenshot_20250408_073355](https://github.com/user-attachments/assets/50dcb56d-bc70-4329-94cb-5b848f265c97)
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![Screenshot_20250408_073322](https://github.com/user-attachments/assets/ba5c519a-bb34-4724-9c14-3278c6c09afd)
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Release Notes:

- N/A

crates/markdown/src/parser.rs

@@ -537,6 +537,28 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_html_comments() {
+        assert_eq!(
+            parse_markdown("  <!--\nrdoc-file=string.c\n-->\nReturns"),
+            (
+                vec![
+                    (2..30, Start(HtmlBlock)),
+                    (2..2, SubstitutedText("  ".into())),
+                    (2..7, Html),
+                    (7..26, Html),
+                    (26..30, Html),
+                    (2..30, End(MarkdownTagEnd::HtmlBlock)),
+                    (30..37, Start(Paragraph)),
+                    (30..37, Text),
+                    (30..37, End(MarkdownTagEnd::Paragraph))
+                ],
+                HashSet::new(),
+                HashSet::new()
+            )
+        )
+    }
+
     #[test]
     fn test_plain_urls_and_escaped_text() {
         assert_eq!(