fix(pcan): swap SetValue and GetErrorText docstrings (#2058)

* fix(pcan): swap SetValue and GetErrorText docstrings

The docstrings for SetValue and GetErrorText in pcan/basic.py were
swapped: SetValue described returning an error text and GetErrorText
described configuring a channel value. Swap them so each docstring
matches its function.

Fixes #2047

* ci: retrigger flaky test_send_periodic_duration

Signed-off-by: Sai Asish Y <say.apm35@gmail.com>

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Signed-off-by: Sai Asish Y <say.apm35@gmail.com>