`'sample_rate'` is deprecated, but pyedflib still uses it internally

[cbrnr]

I am using highlevel.write_edf() in my tests, and even though I am passing sample_frequency instead of sample_rate, I still get a DeprecationWarning:

    def test_read_shhs(tmp_path):
        """Basic sanity checks for records read via read_shhs."""
        durations = [0.1, 0.2]  # hours
        valid_stages = {int(s) for s in SleepStage}
    
>       _create_dummy_shhs(data_dir=tmp_path, durations=durations)

sleepecg/test/test_sleep_readers.py:157: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
sleepecg/test/test_sleep_readers.py:124: in _create_dummy_shhs
    _dummy_nsrr_edf(f"{edf_dir}/{record_id}.edf", hours, ecg_channel="ECG")
sleepecg/test/test_sleep_readers.py:29: in _dummy_nsrr_edf
    highlevel.write_edf(filename, ecg, signal_headers)
.direnv/python-3.10.10/lib/python3.10/site-packages/pyedflib/highlevel.py:486: in write_edf
    f.setSignalHeaders(signal_headers)
.direnv/python-3.10.10/lib/python3.10/site-packages/pyedflib/edfwriter.py:351: in setSignalHeaders
    self.update_header()
.direnv/python-3.10.10/lib/python3.10/site-packages/pyedflib/edfwriter.py:249: in update_header
    self._calculate_optimal_record_duration()
.direnv/python-3.10.10/lib/python3.10/site-packages/pyedflib/edfwriter.py:922: in _calculate_optimal_record_duration
    all_fs = [self._get_sample_frequency(i) for i,_ in enumerate(self.channels)]
.direnv/python-3.10.10/lib/python3.10/site-packages/pyedflib/edfwriter.py:922: in <listcomp>
    all_fs = [self._get_sample_frequency(i) for i,_ in enumerate(self.channels)]
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <pyedflib.edfwriter.EdfWriter object at 0x7ff705cb0370>, channelIndex = 0

    def _get_sample_frequency(self, channelIndex):
        # Temporary conditional assignment while we deprecate 'sample_rate' as a channel attribute
        # in favor of 'sample_frequency', supporting the use of either to give
        # users time to switch to the new interface.
        if 'sample_rate' in self.channels[channelIndex]:
>           warnings.warn("`sample_rate` is deprecated and will be removed in a future release. \
                          Please use `sample_frequency` instead", DeprecationWarning)
E           DeprecationWarning: `sample_rate` is deprecated and will be removed in a future release.                           Please use `sample_frequency` instead

Currently, users cannot really prevent that warning even if they have already switched to the new sample_frequency.