Obsolete PRs are not auto-closed

How to reproduce

1. Revert the commit Remove version constraints for postgres and mysql
2. Run renovate once. It will create a PR for lock file maintenance
3. Undo (revert) the revert.
4. Run renovate again. The PR will stay open with conflicts.

I struggled to reproduce this behavior until I noticed that the broken PR in our prod repository was for "lock file maintenance". Once I added config for lock file maintenance to renovate.json, deleted existing PRs and branches and retried I was able to reproduce.

This was the command I used to run renovate:

#!/usr/bin/env bash
set -euo pipefail

export GITHUB_COM_TOKEN=$RENOVATE_TOKEN

docker run \
    --rm \
    -e LOG_LEVEL="debug" \
    -e RENOVATE_TOKEN \
    -e GITHUB_COM_TOKEN \
    renovate/renovate \
    --dry-run="false" \
    --schedule= --pr-hourly-limit= --force-cli \
    --autodiscover \
    --autodiscover-filter "pascal-hofmann/renovate-minimal-reproduction-26195"

Current behavior

PR stays open with conflicts.

Expected behavior

PR is auto-closed.