Fix cache cleanup script (now tested to work)

[corneliusroemer]

Fixing the cleanup-cache action.

Background

Unfortunately the script as shown in Github docs doesn't work

https://github.com/loculus-project/loculus/actions/runs/7873524962/job/21481061540

gh extension install actions/gh-actions-cache
  
  echo "Fetching list of cache key"
  cacheKeysForPR=$(gh actions-cache list -R $REPO -B $BRANCH -L 100 | cut -f 1 )
  
  ## Setting this to not fail the workflow while deleting cache keys.
  set +e
  echo "Deleting caches..."
  for cacheKey in $cacheKeysForPR
  do
      gh actions-cache delete $cacheKey -R $REPO -B $BRANCH --confirm
  done
  echo "Done"
  shell: /usr/bin/bash -e {0}
  env:
    GH_TOKEN: ***
    REPO: loculus-project/loculus
    BRANCH: refs/pull/98[4](https://github.com/loculus-project/loculus/actions/runs/7873524962/job/21481061540#step:2:4)/merge
Fetching list of cache key
Error: Resource not accessible by integration
Deleting caches...
Done

Testing

Can be tested with:

gh workflow run --ref corneliusroemer-patch-1 

[corneliusroemer]

Cool it works now: https://github.com/loculus-project/loculus/actions/runs/7874777435/job/21485167122