Hide unbuilt versions in footer flyout

[santos22]

Should fix #6971

This also assumes the latest version has built=True, which I'm not sure is the case in production.

[santos22]

The following might need to be updated in test_version_queries to include built=True:

self.pip.versions.create(
    verbose_name=identifier,
    identifier=identifier,
    type=TAG,
    active=True,
    built=True,
)

[stsewd]

@santos22 yeah, is fine to update those tests.

[santos22]

Updated the test 👍

[santos22]

There was a line that was too long - is the following okay for the lint check?

def public(self, user=None, project=None, only_active=True,
           include_hidden=True, only_built=False):

[stsewd]

@santos22 yeah, that works

[stsewd]

LGTM!, thanks!