python3-bcrypt: enable build of unit tests

python3-bcrypt: enable build of unit tests

The source code of bcrypt extension doesn't define any tests
but it is to show the ptest-cargo usage

Below is the updated test suite output for the recipe (cut):

PASS: tests/test_bcrypt.py:test_invalid_params[password-$2b$04$cVWp4XaNU8a4v1uMRum2SO-513-10-ValueError]
PASS: tests/test_bcrypt.py:test_invalid_params[password-$2b$04$cVWp4XaNU8a4v1uMRum2SO-20-0-ValueError]
PASS: tests/test_bcrypt.py:test_2a_wraparound_bug
============================================================================
Testsuite summary

running 0 tests

test result: ok$<2>. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.01s

root@qemux86-64:/usr/lib/python3-bcrypt/ptest#

Signed-off-by: Frederic Martinsons <frederic.martinsons@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>