Release of v2.3.1

[elrayle]

v2.3.1 has been released. The primary changes include:

• update to the latest official SPDX license data
• add nightly cron job to fetch latest official SPDX license data and if there are changes, create a PR to update go-spdx to use those licenses

The later will make staying on top of SPDX released licenses much easier. I am very excited about having that in place.

NOTE: There was also a release v2.3.0. It updated to Go 1.22 which led to some challenges for downstream users. The release was reverted and v2.3.1 returns to Go 1.21.