Fix pytest config for new pytest 9.0 release (pvlib#2596)

* adapt pytest config to work with pytest 9.0

* whatsnew

Author: kandersolar

docs/sphinx/source/whatsnew/v0.13.2.rst

@@ -53,6 +53,8 @@ Documentation
 
 Testing
 ~~~~~~~
+* Update pytest configuration in ``pyproject.toml`` to work with pytest 9.0.
+  (:pull:`2596`)
 
 
 Benchmarking

pyproject.toml

@@ -99,7 +99,9 @@ pvlib = ["data/*"]
 
 [tool.pytest]
 junit_family = "xunit2"
-testpaths = "tests"
+testpaths = [
+    "tests"
+]
 # warning messages to suppress from pytest output.  useful in cases
 # where a dependency hasn't addressed a deprecation yet, and there's
 # nothing we can do to fix it ourselves.