Fix failing develop with mis-matched snapshots

Date separator markup updated in #10404

While some new snapshot tests added in #10353

Author: MadLittleMods

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
-              aria-hidden="true"
+            <div
+              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"
             />