Scan five years of CVEs for new PoCs, not two

Discovery only looked at the current year and the one before it, so a PoC
published this week for a 2023 CVE was never found. Exploits for older
vulnerabilities keep appearing, and the daily run has budget to spare: the
window is still three days, so the cost is five sets of search terms instead
of two against the same short window.

.github/workflows/sync_cve_pocs.yml

@@ -27,7 +27,7 @@ jobs:
       - name: Discover and ingest CVE PoCs
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
-        run: python3 scripts/update_cves.py --lookback-days 3 --years 2
+        run: python3 scripts/update_cves.py --lookback-days 3 --years 5
 
       - name: Check for changes and commit
         run: |