test: suppress one more EncodingWarning #1966

Without this, I got:

```
tests/test_oddball.py::DoctestTest::test_doctest
  /usr/local/pyenv/pyenv/versions/3.10.17/lib/python3.10/pdb.py:160: EncodingWarning: 'encoding' argument not specified
    with open(os.path.expanduser('~/.pdbrc')) as rcFile:
```

Author: nedbat

CHANGES.rst

@@ -23,8 +23,12 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- A number of EncodingWarnings were fixed that could appear if you've enabled
+  PYTHONWARNDEFAULTENCODING, fixing `issue 1966`_.  Thanks, `Henry Schreiner
+  <pull 1967_>`_.
 
+.. _issue 1966: https://github.com/nedbat/coveragepy/issues/1966
+.. _pull 1967: https://github.com/nedbat/coveragepy/pull/1967
 
 .. start-releases
 

CONTRIBUTORS.txt

@@ -95,6 +95,7 @@ Greg Rogers
 Guido van Rossum
 Guillaume Chazarain
 Guillaume Pujol
+Henry Schreiner
 Holger Krekel
 Hugo van Kemenade
 Ian Moore

tests/test_oddball.py

@@ -8,6 +8,7 @@
 import os.path
 import re
 import sys
+import warnings
 
 from flaky import flaky
 import pytest
@@ -465,7 +466,11 @@ def return_arg_or_void(arg):
             doctest.testmod(sys.modules[__name__])  # we're not __main__ :(
             ''')
         cov = coverage.Coverage()
-        self.start_import_stop(cov, "the_doctest")
+        with warnings.catch_warnings():
+            # Doctest calls pdb which opens ~/.pdbrc without an encoding argument,
+            # but we don't care. PYVERSIONS: this was needed for 3.10 only.
+            warnings.filterwarnings("ignore", r".*'encoding' argument not specified.*")
+            self.start_import_stop(cov, "the_doctest")
         data = cov.get_data()
         assert len(data.measured_files()) == 1
         lines = sorted_lines(data, data.measured_files().pop())

tox.ini

@@ -31,7 +31,7 @@ setenv =
     # We want to know about missing encoding arguments, but we need to silence
     # some warnings that aren't ours.  We can't silence them in 3.9 because
     # EncodingWarning doesn't exist yet, and it's hard to suppress them in some
-    # environments and not others.  So by default, don't warn, and will enable
+    # environments and not others.  So by default, don't warn, and we'll enable
     # the warning in a handful of environments to catch the problems.
     PYTHONWARNDEFAULTENCODING=
     py3{10,11,12,13,14}: PYTHONWARNDEFAULTENCODING=1