Pending transactions do not block their replacement counterparts

[iamacook]

Description

Pending replacement transactions do not block the execution button on transactions that are being replaced.

Steps to reproduce

1. Create a transaction and a related (rejection) replacement one.
2. Execute one of the two and observe that the collapsed execute action is not blocked.

Expected result

The non-pending transaction should have a strikethrough and actions be blocked.

Obtained result

The non-pending transaction can be executed and hovering on it blocks the currently pending transaction.

[francovenica]

Looks good to me

Created a tx and its rejection side by side, making sure that during the process of executing one blocks the other
Tested also with other side-by-side tx (not only rejections)
Refreshed the page making sure that this status of "blocked while other executes" persists.