chore: migrate github-actions updates from dependabot to renovate

[glokos]

Add a github-actions-only Renovate config

What this is

Renovate is a bot that opens PRs to update your
dependencies. This config scopes it to GitHub Actions only — it watches the
uses: lines in .github/workflows/* and opens a PR when an action has a newer
version.

Once merged (and the Renovate app runs), you'll get PRs like
"deps(actions/checkout): update to v5" — SHA-pinned, weekly, batched.

Why Renovate over Dependabot

Both work; we picked Renovate for what this specific config needs:

• SHA-pinning + keep the version comment — Renovate rewrites
  uses: actions/checkout@v4 to uses: actions/checkout@<sha> # v4.2.2. Pinning
  to a SHA is the
  GitHub-recommended
  supply-chain hardening; Dependabot can't pin and keep the readable version
  comment.
• minimumReleaseAge: 14 days — skips releases younger than two weeks, so a
  compromised/yanked action version never lands automatically. Dependabot has no
  equivalent cooldown.
• One config, one bot org-wide — the rest of CoW's repos already standardize
  on Renovate (the infrastructure repo drives ansible image bumps through it),
  so this keeps a single tool and PR style everywhere instead of splitting
  Actions onto Dependabot.

Dependabot is the right call if you want zero setup and GitHub-native — it just
can't do the SHA-pin-with-comment or the release-age delay we want here.

How to test it works

You don't need to wait for the weekly schedule:

1. Merge the PR. Config does nothing until it's on the default branch.
2. Confirm the app is installed — an admin checks
   github.com/organizations/cowprotocol/settings/installations
   → Renovate → this repo is in its scope. (This is the one real prerequisite —
   a committed config is inert without the app.)
3. Force a run — on the Renovate app dashboard, or push a temporary workflow
   line that uses an outdated action (e.g. actions/checkout@v3).
4. Look for the Dependency Dashboard issue Renovate opens on first run
   (titled "Dependency Dashboard"), plus any "deps(...)" PRs. Seeing them =
   working. The dashboard lists everything it detected and will update.

Quick local check of just the config syntax (doesn't test behavior):

npx --yes --package renovate renovate-config-validator .github/renovate.json5

[gemini-code-assist]

Code Review

This pull request replaces the Dependabot configuration with a new Renovate configuration (.github/renovate.json5) targeting GitHub Actions. However, this change completely disables automated updates for npm and uv dependencies in the /dev directory. It is recommended to either migrate these ecosystems to Renovate or retain Dependabot to manage them.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.