Enable monthly dependabot updates for the linters

[garrison]

This enables monthly dependabot updates for all packages whose versions are precisely pinned in pyproject.toml, which for us is various linters. This way, we will have a sense of (i) which linters have updates available; (ii) which linters can be updated immediately without causing any errors; and (iii) when a linter can't be immediately updated, an automated CI log of what first needs to be fixed. I believe monthly is the appropriate cadence for these checks; I really don't want to be bothered more often than that with linter updates, but I don't want them to get way out of date either without us noticing.

One thing that might become annoying is various black updates, but if that occurs we can later tell dependabot to ignore them.

I first experimented with this on a personal fork of ckt. See here for the activity that dependabot created on my repository. The only difference with this PR is that the PRs here (and there going forward) will have the label dependencies but not the label python, since labels is explicitly provided in the yml.

[github-actions]

Pull Request Test Coverage Report for Build 4684976614

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.59%

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Totals
Change from base Build 4672713865:	0.0%
Covered Lines:	1515
Relevant Lines:	1791

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💛 - Coveralls

[garrison]

I added the "on hold" label to this. I think we want to wait until some of the current milestones are met before messing with the linters.

[caleb-johnson]

Cool, thanks

[garrison]

I'm going to merge this now that we have the code migration done. We can always ignore the resulting dependabot PRs if they look like they will require substantial changes. (I doubt they will.)