Lock pip package urllib3 to 1.26.15

plugins/_module/pip_update.py

@@ -25,6 +25,7 @@ def main():
         'borgbackup': '1.1.17',
         'jinja2': '3.0.3',
         'charset-normalizer': '2.0.12',# Certbot fails with 2.1.0
+        'urllib3': '1.26.15',# Certbot fails with 2.0.0
         'blinker': '1.4',# Ubuntu package
         'entrypoints': '0.3',# Ubuntu package
         'pyparted': '3.11.2',