Changes for QuantLib 1.42.1

This is a bug-fix release removing a regression in the Gsr class possibly leading to an infinite notification loop. Thanks to Aleksis Ali Raza for the heads-up.

Full list of pull requests

All the pull requests merged in this release are listed on its release page at https://github.com/lballabio/QuantLib/releases/tag/v1.42.1.

The list of commits since the previous release is available in ChangeLog.txt.