[codex] fix dependabot actions cooldown config

[jgoux]

What changed

Remove the unsupported cooldown.semver-minor-days and cooldown.semver-patch-days settings from the github-actions Dependabot ecosystem.

The Bun ecosystem keeps its cooldown settings, and GitHub Actions updates keep the weekly Tuesday schedule, PR limit, and minor/patch grouping.

Why

Dependabot rejects semver-specific cooldown properties for the github-actions ecosystem with:

The property `#/updates/0/cooldown/semver-minor-days` is not supported for the package ecosystem `github-actions`.
The property `#/updates/0/cooldown/semver-patch-days` is not supported for the package ecosystem `github-actions`.

Removing those keys restores a valid Dependabot config while preserving the grouped weekly update policy.

Validation

• Parsed .github/dependabot.yml successfully as YAML