[fix] Fix pip Py2 deprecation filter in tests

Adapt filter in tests for pip emitting Python2.7 deprecation warnings
to pip >= 20.2.2 and < 21.0 - these versions seem to accidentally add
a redundant bit of message to the warning.

src/zc/buildout/testing.py

@@ -623,14 +623,15 @@ python27_warning = (re.compile(r'DEPRECATION: Python 2.7 reached the end of its
     'life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no '
     'longer maintained. A future version of pip will drop support for Python '
     '2.7. More details about Python 2 support in pip, can be found at '
-    'https://pip.pypa.io/en/latest/development/release-process/#python-2-support\n'),
+    'https://pip.pypa.io/en/latest/development/release-process/#python-2-support\r?\n'),
     '')
 
 python27_warning_2 = (re.compile(r'DEPRECATION: Python 2.7 reached the end of its '
     'life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no '
     'longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. '
-    'More details about Python 2 support in pip, can be found at '
-    'https://pip.pypa.io/en/latest/development/release-process/#python-2-support\n'),
+    'More details about Python 2 support in pip,? can be found at '
+    'https://pip.pypa.io/en/latest/development/release-process/#python-2-support'
+    '( pip 21.0 will remove support for this functionality.)?\r?\n'),
     '')
 
 easyinstall_deprecated = (re.compile(r'.*EasyInstallDeprecationWarning.*\n'),'')