testing/py3-nikola: upgrade to 8.3.1
https://github.com/getnikola/nikola/releases/tag/v8.3.1
Tests were enabled for x86_64 and they pass with some warnings. Please let me know if enabling tests is undesirable, can disable them again. Thanks!
Build has been checked to pass with tests skipped on loongarch64 (thanks to znley).
Edited by mio