fix grammar in test_collect_functools_partial docstr (#5703)

fix grammar in test_collect_functools_partial docstr

Author: nicoddemus

testing/python/collect.py

@@ -1146,7 +1146,7 @@ class Test(object):
 def test_collect_functools_partial(testdir):
     """
     Test that collection of functools.partial object works, and arguments
-    to the wrapped functions are dealt correctly (see #811).
+    to the wrapped functions are dealt with correctly (see #811).
     """
     testdir.makepyfile(
         """