Change sync_github_advisories min_year from 2015 to 2006 to get all GHSA "rubygems" files

[Al Snow]

Let's change the sync_github_advisories's script from
(min_year) 2015 to 2006 to get the remaining 184 GHSA "rubygems" files.
GHSA is "GitHub Security Advisory" database.

[Al Snow]

Now we have 751 "gems" files and 114 "rubies" files for a total of 865 yml files so unclear if this is needed now so closing this issue.