devel/py-super-collections: update to 0.5.5

No changelog provided by upstream.

Most important changes seem to be:

• Fix: Custom JSON encoder does not correctly check datetime object
• Expanded testing

Also remove pytest from port's TEST_DEPENDS as redundant - it is already
implied by USE_PYTHON=pytest.

PR: 289542
Reported by: Vladyslav Movchan <vladislav.movchan@gmail.com> (maintainer)