chore: rm mbt, trace tests from CI; fix dependabot (backport #2000)

[mergify]

Description

Closes: #N/A

MBT is currently deprecated, and the tests fail regularly starting with the upgrade to Cosmos sdk v50.
Trace tests are doing the same work as e2e tests, so we are disabling them for the time being.

Dependabot configuration was broken a couple weeks ago.

For more context, see #1987 for a brief overview of the future plans for randomized testing.

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• Included the correct type prefix in the PR title
• Targeted the correct branch (see PR Targeting)
• Provided a link to the relevant issue or specification
• Reviewed "Files changed" and left comments if necessary
• Confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• Confirmed the correct type prefix in the PR title
• Confirmed all author checklist items have been addressed
• Confirmed that this PR does not change production code

Summary by CodeRabbit

• Chores
  • Removed redundant test-mbt and test-trace jobs from the CI workflow.
  • Adjusted indentation in the .github/dependabot.yml file for better readability.

---

This is an automatic backport of pull request #2000 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of eb93342 has failed:

On branch mergify/bp/release/v5.1.x/pr-2000
Your branch is up to date with 'origin/release/v5.1.x'.

You are currently cherry-picking commit eb93342.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .github/dependabot.yml
	both modified:   .github/workflows/test.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally