ci: remove all existing advisories before generating (#151)

This will help ensure that advisories that are no longer being generated
are not retained in the database, which isn't handled by our scripts
since this situation should only ever happen when we've made a change to
our scripts to fix a bug

Author: G-Rath

.github/workflows/generate.yml

@@ -30,6 +30,7 @@ jobs:
       - run: poetry install
       - run: poetry run scripts/download_sa_advisories.py
       - run: poetry run scripts/precache_nodes.py
+      - run: rm -rf advisories/
       - run: poetry run scripts/generate_osv_advisories.py
       - uses: peter-evans/create-pull-request@c0f553fe549906ede9cf27b5156039d195d2ece0 # v8.1.0
         with: