Update lxml requirement from <=5.2.0 to <=5.2.1 (#202)

Updates the requirements on [lxml](https://github.com/lxml/lxml) to permit the latest version.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-0.5.1...lxml-5.2.1)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

setup.py

@@ -252,7 +252,7 @@ def path_to_src(source_path_list):
        packages = ["PyPop", "PyPop.xslt"],
        package_data={"PyPop.xslt": data_file_paths},
        install_requires = ["numpy <= 1.26.4",
-                           "lxml <= 5.2.0",
+                           "lxml <= 5.2.1",
                            "importlib-resources; python_version <= '3.8'",
                            "importlib-metadata; python_version <= '3.8'"],
        extras_require={