docs(test): correct markdown/defaultBlocks comment about caption survival

Captions on image/video/audio now survive round-trip via raw `<figure>`
HTML — they shouldn't have been listed as a dropped feature.

Author: nperez0111

tests/src/unit/core/formatConversion/exportParseEquality/exportParseEqualityTestInstances.ts

@@ -957,8 +957,9 @@ export const exportParseEqualityTestInstancesMarkdown: TestInstance<
   {
     // Mirrors the default-blocks demo (examples/01-basic/04-default-blocks)
     // so we get a single round-trip snapshot covering every default block
-    // type. Markdown is lossy (colors/alignment/captions/file blocks/toggle
+    // type. Markdown is lossy (colors/alignment/file blocks/toggle
     // affordances are dropped), so the snapshot documents what survives.
+    // Image/video/audio captions are preserved via raw `<figure>` HTML.
     testCase: {
       name: "markdown/defaultBlocks",
       content: [