Ignore warnings about pkg_resources in tests

This MR updates the pytest configuration to ignore warnings about pkg_resources; we don't use it, but it is now deprecated.

pyproject.toml

@@ -19,4 +19,5 @@ source = ["gwdatafind"]
 addopts = "-r a --color=yes"
 filterwarnings = [
 	"error",
+	"ignore:.*pkg_resources"
 ]