heyoka 7.2.1

[bluescarni]

This is a quick bugfix release that works around a thread safety issue in the erfa routines on top of which UTC/TAI conversions are implemented.

As usual, the full changelog is available here:

https://bluescarni.github.io/heyoka/changelog.html

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This discussion was created from the release heyoka 7.2.1.