Fix failing tests

[gbolmier]

Some tests are failing due to segmentation fault in the ubuntu-latest environment of the github action runners (no pb locally).

Search for Fatal Python error: Aborted in the logs:

• Current thread 0x00007ff6e5b7db80 (most recent call first):
  File "/home/runner/work/river/river/river/stats/test_stats.py", line 43 in test_pickling

• Current thread 0x00007faceb0aeb80 (most recent call first):
  File "/opt/hostedtoolcache/Python/3.12.3/x64/lib/python3.12/copy.py", line 151 in deepcopy

Potentially helpful:

• Debugging a pytest segfault
• pytest-dev/pytest#8841

Tried to fix by installing Qt dependencies, but it didn't change anything.

See discord thread.

[smastelini]

A lot of the crashes happen in picking-related stuff, but this might not be related

[gbolmier]

Fixed by #1564.