chore: use pathlib.read_text

This avoids having a resource warning when installing.

setup.py

@@ -1,6 +1,8 @@
 from setuptools import find_packages
 from setuptools import setup
 
+from pathlib import Path
+
 
 version = "3.0.1.dev0"
 
@@ -9,11 +11,13 @@
     "plone.testing",
 ]
 
+long_description = f"{Path('README.rst').read_text()}\n{Path('CHANGES.rst').read_text()}"
+
 setup(
     name="plone.resource",
     version=version,
     description="Static files for Plone",
-    long_description=(open("README.rst").read() + "\n" + open("CHANGES.rst").read()),
+    long_description=long_description,
     long_description_content_type="text/x-rst",
     classifiers=[
         "Development Status :: 5 - Production/Stable",