Skip the linkify test by default.

[tsutsu3]

Context

I see issues that test fails due to lack of linkify-it-py. #312 #167 #191
With the default parser (commonmark), it works without linkify-it-py.
How about making the test also work without linkify-it-py by default?

Proposal

pytest tests: Run tests (skip linkify tests)
pytest tests --all: Run all tests (with linkify tests)

Tasks and updates

No response

[chrisjsewell]

No that's ok, these are all just issues from the same guy, that doesn't install the proper test dependencies