Add compatibility with newer versions of pytest.

Taken from upstream:

  https://github.com/dateutil/dateutil/commit/2bdd63158b7f981fc6d70a869680451bdfd8d848

diff --git a/dateutil/test/test_internals.py b/dateutil/test/test_internals.py
index 53081314..b32e6723 100644
--- a/dateutil/test/test_internals.py
+++ b/dateutil/test/test_internals.py
@@ -9,6 +9,7 @@
 
 import sys
 import pytest
+import warnings
 
 from dateutil.parser._parser import _ymd
 from dateutil import tz
@@ -65,18 +66,17 @@ def test_parser_parser_private_not_warns():
     from dateutil.parser._parser import _timelex, _tzparser
     from dateutil.parser._parser import _parsetz
 
-    with pytest.warns(None) as recorder:
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
         _tzparser()
-        assert len(recorder) == 0
 
-    with pytest.warns(None) as recorder:
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
         _timelex('2014-03-03')
 
-        assert len(recorder) == 0
-
-    with pytest.warns(None) as recorder:
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
         _parsetz('+05:00')
-        assert len(recorder) == 0
 
 
 @pytest.mark.tzstr
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<tr><td><span title='2023-03-13 15:08:34 +0100'>2023-03-13</span></td><td><a href='/guix/commit/gnu/packages/pumpio.scm?id=7b743d4f6864427883766f1d9657f8c106cb83c0'>gnu: pumpa: Update upsream URL.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes &lt;http://issues.guix.gnu.org/issue/52257&gt;.

* gnu/packages/pumio.scm (pumpa)[source]: Replace pumpa origin.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Sarthak Shah</td></tr>
<tr><td><span title='2023-03-04 18:46:37 +0100'>2023-03-04</span></td><td><a href='/guix/commit/gnu/packages/pumpio.scm?id=0d6c5e0ba1bd6800712e79964f7b9f5c6043f249'>gnu: Remove and deprecate tidy for tidy-html</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/web.scm (tidy): Change to deprecated alias for tidy-html
* gnu/packages/pumpio.scm (pumpa): Use tidy-html instead of tidy and correct
header name.
* gnu/packages/markup.scm (hoedown):
* gnu/packages/photo.scm (enblend-enfuse):
* gnu/packages/php.scm (php):
* gnu/packages/python-xyz.scm (python-pytidylib):
Use tidy-html instead of tidy.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Morgan Smith</td></tr>