Nightly Trigger Update, 21.2 branch (2024.02.08.)

Synchronized Athena/version.txt with AnalysisBase/version.txt. Purely to trigger a new nightly build for @robouque for Friday, as discussed on ATLINFR-5242. 😉

@aundrus, I only saw your message on JIRA now. 😦 I'll just merge this in quickly, now that I already set everything up...