Release 3.1.0

• The repository has been moved to github.com/gocsaf/csaf and thus uses a new go module path.
• Uses a custom HTTP user-agent header by default.
• Avoids a race condition when downloading in parallel (#546).
• Turns missing an OpenPGP fingerprint into a warning (#555).
• Checking several domains in one command line call works better (#523).
• Utilizes currently maintained go version 1.22 (#573).
• Switched licenses of original content from MIT to Apache2.0.
• 13 Issues were closed.
• 28 PRs were merged.