fix(Dockerfile): allow running commands with docker run

[vringar]

According to https://gitlab.com/gitlab-org/gitlab-runner/-/issues/2109#note_47480476 adding the "-c" to the ENTRYPOINT is necessary to be able to run commands like docker run libafl "cargo build"

[addisoncrump]

Thanks for your PR! You might get a couple emails about "CI pipeline was cancelled", I'm just cancelling the runs for the CI that you've force-pushed over to save us some resources.

[vringar]

Sorry about the force push, I copied over the -l without understanding what it does and it broke the external command invocation.

[addisoncrump]

All good, I do it all the time :sweat_smile: To be honest, the reason is that we have three or four active PRs right now and only a few runners, so I was just pruning so everybody's CI finished within the next hour lol