[Pre585] Write a lint check for: multiple-cve-1-ghsa-in-1-dir in support of issue #580

Write a lint check for: multiple-cve-1-ghsa-in-1-dir in support of issue #580.
```
git grep "^ghsa:" |sed -e "s,CVE-.*ghsa:,," |sort |uniq -d
```
This script found the advisories fixed in #660.
