Make publishPost e2e util more resilient

[ntsekouras]

Recently with a failure in e2e tests it was discovered that the e2e util publishPost can be augmented to make sure the publish post action has been performed.

Currently the util relies on waiting for the snackbar to exist, but after #34731 a snackbar is shown in other cases as well - like saving a draft. This can create unexpected results with race conditions.

Some attempts were 2d135c4 and #35579 with no success.

[Mamaduka]

@ntsekouras, is this still an issue after the Playwright migration?

[ntsekouras]

Let's close this one, yes.