Don't use relative fixture path

[joshmoore]

see: #1312
see: #1347
see: #1348

Attempting to make conda-forge happy again.

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

Merging #1364 (6ddb9bd) into main (eacda8d) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main     #1364   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           36        36           
  Lines        14802     14803    +1     
=========================================
+ Hits         14802     14803    +1     

Impacted Files	Coverage Δ
zarr/tests/test_attrs.py	100.00% <100.00%> (ø)