ci(renovate): enable submodule updates (backport #765)

[mergify]

Welcome to Cryostat! 👋

Before contributing, make sure you have:

• Read the contributing guidelines
• Linked a relevant issue which this PR resolves
• Linked any other relevant issues, PR's, or documentation, if any
• Resolved all conflicts, if any
• Rebased your branch PR on top of the latest upstream main branch
• Attached at least one of the following labels to the PR: [chore, ci, docs, feat, fix, test]
• Signed all commits using a GPG signature

To recreate commits with GPG signature git fetch upstream && git rebase --force --gpg-sign upstream/main

---

See cryostatio/cryostat#1356

---

This is an automatic backport of pull request #765 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 08b74af has failed:

On branch mergify/bp/cryostat-v4.1/pr-765
Your branch is up to date with 'origin/cryostat-v4.1'.

You are currently cherry-picking commit 08b74af.
  (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/rm <file>..." as appropriate to mark resolution)
	deleted by us:   .github/renovate.json

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