fix(unit_test): prevent logging from raising exceptions after tests

pytest's capsys just closes the stdout when done with tests. there are
issues tracking this problem, see pytest-dev/pytest#5577 .
but we adds a handler which redirect the logging messages to stdout. so,
once pytest finishes testing, exceptions are raised when writing logging
messages, like
```
22:37:20    File "/usr/local/lib/python3.10/logging/__init__.py", line 1101, in emit
22:37:20      stream.write(msg + self.terminator)
22:37:20  ValueError: I/O operation on closed file.
```
so, in this change, `logging.raiseExceptions` is disabled when pytest's
session finishes.

Fixes #6000

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

unit_tests/conftest.py

@@ -142,3 +142,14 @@ def fixture_params(request: pytest.FixtureRequest):
 @pytest.fixture(scope='function', autouse=True)
 def fixture_cleanup_continuous_events_registry():
     ContinuousEventsRegistry().cleanup_registry()
+
+
+def pytest_sessionfinish():
+    # pytest's capsys is enabled by default, see
+    # https://docs.pytest.org/en/7.1.x/how-to/capture-stdout-stderr.html.
+    # but pytest closes its internal stream for capturing the stdout and
+    # stderr, so we are not able to write the logger anymore once the test
+    # session finishes. see https://github.com/pytest-dev/pytest/issues/5577,
+    # to silence the warnings, let's just prevent logging from raising
+    # exceptions.
+    logging.raiseExceptions = False