Update znflow

[PythonFZ]

Use new ZnFlow version that supports __add__

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@fb922c6). Click here to learn what that means.
The diff coverage is 76.92%.

❗ Current head 222df5b differs from pull request most recent head e864fbd. Consider uploading reports for the commit e864fbd to get more accurate results

@@           Coverage Diff           @@
##             main     #548   +/-   ##
=======================================
  Coverage        ?   89.63%           
=======================================
  Files           ?       19           
  Lines           ?     1254           
  Branches        ?      455           
=======================================
  Hits            ?     1124           
  Misses          ?      129           
  Partials        ?        1           

Flag	Coverage Δ
fulltest	88.19% <76.92%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
zntrack/fields/zn/__init__.py	92.36% <76.92%> (ø)

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