licensecheck CI job unnecessarily installs the whole project and accesses the CI cache

The problem

The CI runners are on their knees, apparently due to very long load/update times for the CI cache reads. (Addressing this will be another issue.)

Based on the current, shared default configuration, the (systematically run) licensecheck job currently uses the CI cache and installs the full generated-text-detection project yet it only needs access to the pyproject.toml file to run and licensecheck can be run via pipx run licensecheck.

Solution

Update the licensecheck CI job to only run licensecheck via pipx, without installing the whole project and without reading any cache.

Motivation

These updates should reduce the load on the runners induced by these jobs (potentially by 1/3, given that most of the time seems to be spent in loading/updating caches).