Revert changes to nightly fetch script; remove duplicate line

Author: a1icja

.github/workflows/fetch-ci-nightly-data.yaml

@@ -24,11 +24,12 @@ jobs:
           git config --global user.email "<gha@runner>"
           git fetch --all
           git checkout latest-dashboard-data
+          # back out whatever data was there
+          git reset HEAD~1
           # pull in the latest changes
           git pull
           # overwrite the old data
-          git rm -r --cached data/
-          rm -rf data/
+          git rm -r data/
           mkdir -p data/
           mv tmp-data.json data/job_stats.json
           # commit