Fix failing develop with mis-matched snapshots (#10411)

- `develop` failure: 7853678384
 - What happened?
    - Date separator markup updated in https://github.com/matrix-org/matrix-react-sdk/pull/10404
    - While some new snapshot tests added and merged in https://github.com/matrix-org/matrix-react-sdk/pull/10353
 - Merge trains could have helped

test/components/structures/__snapshots__/MessagePanel-test.tsx.snap

@@ -47,11 +47,16 @@ exports[`MessagePanel should handle lots of membership events quickly 1`] = `
             <hr
               role="none"
             />
-            <h2
+            <div
-              aria-hidden="true"
+              class="mx_DateSeparator_dateContent"
             >
-              Thu, Jan 1 1970
+              <h2
-            </h2>
+                aria-hidden="true"
+                class="mx_DateSeparator_dateHeading"
+              >
+                Thu, Jan 1 1970
+              </h2>
+            </div>
             <hr
               role="none"
             />