Update latest dependency yaml to remove comment about keeping branch and set delete-branch to true

[angela97lin]

• Removes the line "Please do not delete the latest-dep-update branch because it's needed by the auto-dependency bot." since it doesn't seem to be true. We don't even have that branch available: https://github.com/alteryx/evalml/branches/all?query=latest-dep-update
• Adds a new configuration that auto-deletes the branch when merging or closing the PR so we don't end up with too many dependency update branches that are stale.
• Updates auto approving to run when unit tests. Here's an example in the featuretools repo: Automated Latest Dependency Updates featuretools#1830

Sample PR looks like: #3213. I closed the PR but don't see the branch auto-delete. :( According to this issue:

When delete-branch is set to true the action will delete the branch in two situations:

If the action is closing the pull request itself (because there is no longer any diff)
If the branch remains in the remote, but there are no further changes. In this case, most likely it has been left undeleted after merging.
Your expectation seems to be that the branch should be deleted immediately after merge, but that's not how it works. The action will find and delete it next time it runs.

[codecov]

Codecov Report

Merging #3212 (7f00798) into main (76661ac) will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main   #3212   +/-   ##
=====================================
  Coverage   99.8%   99.8%           
=====================================
  Files        326     326           
  Lines      31395   31395           
=====================================
  Hits       31304   31304           
  Misses        91      91           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 76661ac...7f00798. Read the comment docs.

[gsheni]

Suggested change

	reviewers: angela97lin, dsherry, jeremyliweishih, freddyaboulton, bchen1116, chukarsten, ParthivNaresh
	reviewers: machineAYX

[gsheni]

I haven't seen this work on repos yet, so I was waiting until it did before adding it here. In the meantime, I would suggest keeping the schedule

[angela97lin]

Oh saddo. Okay, good to know!