PR: Fix focus when debugging cells

[impact27]

Description of Changes

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

Issue(s) Resolved

Fixes #

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[ccordoba12]

Hey @impact27, thanks a lot for your help with this! I just checked in the latest 5.x and it seems this fix is also necessary there (i.e. debugcell is not preserving focus as it should). So, I'm going to move your PR to that branch and then merge it to make our tests pass in master again.

By the way, this is failing in master because the global debug toolbar now has only two actions and we're using the second one (i.e. Debug cell in master) in test_focus_to_editor.

[ccordoba12]

Thanks @impact27!