I don't know why yet, but TEST-73-LOCALE can take more than 10
minutes. Until we figure out why, let's give it a higher priority
so it doesn't bottleneck the test run.
Let's make this behave more like all the rest of the meson stuff.
This also is the first step to making it a bit more flexible so we
can define integration tests in different ways as will be seen in
the next commits.