[MM-36481] Fix emoji regex to support thumbsup (#17846)

model/emoji_test.go

@@ -50,6 +50,9 @@ func TestEmojiIsValid(t *testing.T) {
 	emoji.Name = "name-"
 	require.Nil(t, emoji.IsValid())
 
+	emoji.Name = "name+"
+	require.Nil(t, emoji.IsValid())
+
 	emoji.Name = "name_"
 	require.Nil(t, emoji.IsValid())