fix(tests): use importlib resources to refer to fixture data

Signed-off-by: Cameron Smith <cameron.ray.smith@gmail.com>

src/pyrovelocity/tests/plots/conftest.py

@@ -1,10 +1,13 @@
+from importlib.resources import files
+
 import pytest
 
 from pyrovelocity.io.serialization import load_anndata_from_json
 
 
 @pytest.fixture
 def adata_preprocessed():
-    return load_anndata_from_json(
-        "src/pyrovelocity/tests/data/preprocessed_3_4.json"
+    fixture_file_path = (
+        files("pyrovelocity.tests.data") / "preprocessed_3_4.json"
     )
+    return load_anndata_from_json(fixture_file_path)