The test `--test-show-details=direct` switch should imply `-j1`

[erikd]

Describe the bug

I like using the --test-show-details=direct switch because I see my test output and the colours in the test output are preserved. However, if there are more than one test suite, the test suites trash each other's output.

To Reproduce
Using cabal-install 3.0.0.0 from git:

$ git clone https://github.com/erikd/wide-word
$ cd wide-word
$ cabal build
$ cabal test --test-show-details=direct

Expected behavior

The tests should be run one at a time so their output doesn't interleave.

System informataion
N/A

Additional context
N/A

I am going to have a stab at fixing this.