aka: ensure that 'make test' works as expected The cache contains a copy './local' which is - under some circumstance - corrupted. It is not possible to clear the cache [1] (see the top of the page). Ensure that 'make test' works as expected [2] even if - the python interpreter is missing - the virtualenv exists but pyyaml is missing To hardening when the workflow cache fails, this patch adds the new target 'travis.test' into the workflow. This target probes to import a python module 'yaml'. If this fails the virtualenv will be completely new build. [1] https://github.com/actions/cache/issues/2#issuecomment-673493515 [2] https://github.com/searx/searx/pull/2517#discussion_r567240235 Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>