[FIX] mail: indeterministic discuss test

This PR fixes the `Posting message should transform relevant data to emoji`
test that sometimes failed due to a race condition.

The assertion was too strict, this test just needs to check that the
emoji are properly parsed when posting a message.

Fixes runbot error: 20934.

closes odoo/odoo#120769

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/mail/static/tests/discuss_app/discuss_tests.js

@@ -294,7 +294,7 @@ QUnit.test("Posting message should transform relevant data to emoji.", async (as
     await openDiscuss(channelId);
     await insertText(".o-mail-Composer-input", "test :P :laughing:");
     await click(".o-mail-Composer-send");
-    assert.equal($(".o-mail-Message-body").text(), "test 😛 😆");
+    assert.containsOnce($, ".o-mail-Message-body:contains(test 😛 😆)");
 });
 
 QUnit.test(