tox.ini: fix healtcheck -> healthcheck

[akx]

This could maybe fix the flakiness of some of the cluster tests.

Alternate take on #2387.

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

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afterwards / while the PR is open.

Description of change

healtcheck_cmd has been typoed in tox.ini since its inception, making it a no-op.

Some CI is failing right now due to what seems to be failure connecting to cluster nodes, so perhaps waiting for them to be up fixes things.

[dvora-h]

Not relevant anymore (see #2793)