fix(test): rename io_zarr test_round_trip.py to avoid pytest module collision (#1907)

test/mesh has no __init__.py files, so pytest (prepend import mode) maps
test files to bare module names. test/mesh/io/io_zarr/test_round_trip.py
(added in #1894) collides with test/mesh/io/io_pyvista/test_round_trip.py,
aborting collection with 'import file mismatch' in any CI stream that
collects the full tree (first seen in the multigpu-static stream on #1904;
it was not caught on #1894 because the multi-GPU selection gate skipped
that stream).

Author: negin513