tests: More fixes for gjs tests

tests: More fixes for gjs tests

Previous to this commit, the gjs tests were installed-only; and our
logic for handling the "--enable-installed-tests=exclusive" logic
actually also meant they weren't installed.

It did work for me locally with `--enable-installed-tests`.

However, to make things fully symmetric, let's enable the js tests to also be
run under `make check`.

Also remove `corrupt-repo-ref.js` from the PAPR invocation since it's not
actually a unit test, it's a utility helper.

Closes: #1022
Approved by: jlebon