…k objects

…tation means it can no longer just be set to 0 (#10576)

This should fix our failing tests.

Python 3.14.3 has the following in its changelog:

> [gh-142651](python/cpython#142651):
[unittest.mock](https://docs.python.org/3/library/unittest.mock.html#module-unittest.mock):
fix a thread safety issue where
[Mock.call_count](https://docs.python.org/3/library/unittest.mock.html#unittest.mock.Mock.call_count)
may return inaccurate values when the mock is called concurrently from
multiple threads.

As a result, we have to call `reset_mock()` instead of using
`.call_count = 0`. See example
[here](matplotlib/matplotlib#31153).

Tests on my machine showing that this change fixes things, and it's the
only place to fix:
```bash
$ brew upgrade pyenv
$ pyenv install 3.14.3
$ pyenv global 3.14.3
$ tools/venv.py
$ source venv/bin/activate
$ pytest certbot -k "test_rollback_too_many" 
====================================================================== test session starts =======================================================================
platform darwin -- Python 3.14.3, pytest-9.0.2, pluggy-1.6.0
rootdir: /Users/erica/certbot
configfile: pytest.ini
plugins: anyio-4.12.1, xdist-3.8.0, cov-7.0.0
collected 1039 items / 1038 deselected / 1 selected                                                                                                              

certbot/src/certbot/_internal/tests/reverter_test.py .                                                                                                     [100%]

=============================================================== 1 passed, 1038 deselected in 2.94s ===============================================================
$ git grep 'call_count = 0'
$ git checkout main
$ pytest certbot -k "test_rollback_too_many"
====================================================================== test session starts =======================================================================
platform darwin -- Python 3.14.3, pytest-9.0.2, pluggy-1.6.0
rootdir: /Users/erica/certbot
configfile: pytest.ini
plugins: anyio-4.12.1, xdist-3.8.0, cov-7.0.0
collected 1039 items / 1038 deselected / 1 selected                                                                                                              

certbot/src/certbot/_internal/tests/reverter_test.py F                                                                                                     [100%]

============================================================================ FAILURES ============================================================================
_______________________________________________________ TestFullCheckpointsReverter.test_rollback_too_many _______________________________________________________

self = <certbot._internal.tests.reverter_test.TestFullCheckpointsReverter testMethod=test_rollback_too_many>
mock_logger = <MagicMock name='logger' id='4463351456'>

>   ???
E   AssertionError: assert 2 == 1
E    +  where 2 = <MagicMock name='logger.warning' id='4463351792'>.call_count
E    +    where <MagicMock name='logger.warning' id='4463351792'> = <MagicMock name='logger' id='4463351456'>.warning

certbot/src/certbot/_internal/tests/reverter_test.py:363: AssertionError
==================================================================== short test summary info =====================================================================
FAILED certbot/src/certbot/_internal/tests/reverter_test.py::TestFullCheckpointsReverter::test_rollback_too_many - AssertionError: assert 2 == 1
=============================================================== 1 failed, 1038 deselected in 0.48s ===============================================================
$ git grep 'call_count = 0'
certbot/src/certbot/_internal/tests/reverter_test.py:        mock_logger.warning.call_count = 0
```

…153-on-v3.10.x

Backport PR #31153 on branch v3.10.x (TST: Use correct method of clearing mock objects)