Ignore the `dev_scripts/envs` folder when running tests or linting code,
as it may contain files that are not owned by the current user. In this
case, we've seen that pytest/black etc. fail.
This typically happens when the user has run Dangerzone in a
containerized environment (see #286), and Podman created a directory
with files owned by the user in the nested container.
Instability in the automated tests sometimes would sometimes fail when
running "podman images --format {{.ID}}". It turns out that in versions
prior to podman 4.3.0, podman volumes (stored in
~/.local/share/contaiers) would get corrupted when multiple tests were
run in parallel.
The current solution is to wrap the test command to run sequentially in
versions prior to the fix and in parallel for versions after that.
Fixes#217
Run Mypy static checks against our tests. This brings them inline with
the rest of the codebase, and we have an extra level of certainty that
the tests (and unit tests in particular) will not significantly diverge
from the code they are testing.
