cync_lan (Home Assistant custom_component) v2.10.1

An OTP starting with 0 could never complete setup. The flow collects the
code as a string and then cast it with int() before handing it over, so
012345 went out as 12345; the vendor rejected five digits as invalid, and
retyping the same correct code failed identically every time with nothing to
suggest why. Roughly one code in ten starts with a zero.

Found while merging @baudneo's
cync-lan-lib#1 - he flagged
the same bug in the library, and fixing it there (0.10.1, which this now
requires) only helps if this end stops destroying the zero first. Both halves
were needed.

While covering it, test_otp_step_cannot_connect turned out to assert
invalid_otp - the opposite of its own name. It passed only because
int("not-a-number") raised ValueError before send_otp was ever reached,
so the mocked error it exists to test was never exercised. Corrected, and the
invalid_otp path it had been accidentally covering now has a test of its own.

requirements_test.txt tracks the manifest exactly again.