sysutils/ups-nut: Update to 2.8.4

Release notes for NUT 2.8.4 - what's new since 2.8.3
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https://github.com/networkupstools/nut/milestone/9

 - New NUT drivers:
   * Introduced a `ve-direct` driver for Victron Energy UPS/solar panels
     monitoring. Most specific reported values are in an `experimental.*`
     namespace, as a community we need to come up with standard naming for
     those via `docs/nut-names.txt`. [#440]
   * Introduced a `nutdrv_hashx` driver for numerous devices from Ablerex,
     Atlantis Land, Epyc, Infosec, ION, PowerWalker, Right Power Technology,
     Salicru, UPS Solutions and other vendors (originally shipped with a
     "PowerMaster+", "PowerMaster" or "PowerGuide" software companion suite).
     This seems to be a protocol developed by Cyber Energy for serial-port
     devices, subsequently used by different vendors in their own products
     or re-branded Cyber Energy creations. [#2940]
   * Introduced a `failover` driver for monitoring multiple UPS driver sockets
     and seamless switching out of UPS data in a failover situation, includes
     support for end-to-end tracked instant commands and also variable updating.
     [#2962]
   * Introduced USB (`powervar_cx_usb`) and Serial (`powervar_cx_ser`) drivers
     for Powervar CUSPP protocol, tested with GTS (USB) and UPM (USB, Serial)
     models. [#2988]

 - NUT Monitor GUI:
   * Ported Python 3 version to Qt6, now shipped alongside Qt5 for systems
     with either or both, maximizing compatibility with old and new setups.
     [#2946]
