Attempt to stabilize a few randomly failing e2e tests

[tdonohue]

Description

This small PR is an attempt to stabilize a few randomly failing e2e tests.

1. Sometimes tests which use the Admin sidebar will fail randomly if the sidebar link is not yet visible when it's clicked on. The first commit in this PR attempts to fix that issue.
2. item-edit.cy.ts will sometimes randomly fail if the tabs have not fully loaded. The second commit attempts to fix this issue by waiting on the current tab to be visible before clicking on it, and then ensuring it's visible again after reload of the page.

Instructions for Reviewers

• This PR only touches e2e tests. If those pass, it can be merged.

[tdonohue]

Merging immediately & porting. Hoping this stabilizes things a bit more (several of these are randomly failing at a greater frequency recently)

[dspace-bot]

Backport failed for dspace-7_x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin dspace-7_x
git worktree add -d .worktree/backport-3842-to-dspace-7_x origin/dspace-7_x
cd .worktree/backport-3842-to-dspace-7_x
git switch --create backport-3842-to-dspace-7_x
git cherry-pick -x 5623cc9221ef55f073d54b30efcf42684e9a4455 7feb9fc617f88f57927eb7d6de7b4ed8fa0ce870

[dspace-bot]

Backport failed for dspace-8_x, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally and resolve any conflicts.

git fetch origin dspace-8_x
git worktree add -d .worktree/backport-3842-to-dspace-8_x origin/dspace-8_x
cd .worktree/backport-3842-to-dspace-8_x
git switch --create backport-3842-to-dspace-8_x
git cherry-pick -x 5623cc9221ef55f073d54b30efcf42684e9a4455 7feb9fc617f88f57927eb7d6de7b4ed8fa0ce870