pin xradar<0.8.0 in tests

[chrishavlin]

This is a temporary fix for #5041 on yt's side that should get tests passing but will need to be updated when a fix on the the arm-pyart side is released (at which point we could pin a min version for arm-pyart for the tests).

[chrishavlin]

just to summarize the confusing dependency resolution (and why I just pinnned xradar here):

• as of this writing arm-pyart (v 1.16.1) depends explicitly on xarray, xradar and implicitly on xarray-datatree (which installs as datatree)
• xradar also depends on xarray-datatree
• xarray-datatree is now deprecated and has been moved to xarray >= 2024.10.0
• xradar >= 0.8.0 requires xarray >= 2024.10.0 to account for the xarray-datatree deprecation, xradar < 0.8 relies on the deprecated xarray-datatree

So effectively arm-pyart currently has both a hard dependency on xradar < 0.8.0 and xarray-datatree and just pinning xradar < 0.8.0 is sufficient for yt's tests.

Moving forward, the simplest thing to do will be to replace the change in this PR with a test requirement on arm-pyart >= 1.16.2 after it is released (and assuming it contains a fix).

[neutrinoceros]

Thanks a lot for the write up, I was really confused by this situation.