On a fast laptop, this test currently takes about 7s to run, which is a
significant portion of the overall test suite time.
On a slower CI machine, especially running the test under valgrind, the
test can time out.
There’s no need to always run so many iterations: we run the tests under
CI so often that it’s likely a failure will eventually be hit (if there
is a bug) even with fewer iterations. We also now run the tests once a
week with `-m slow`, so the original iteration count will also still be
used then.
Signed-off-by: Philip Withnall <pwithnall@gnome.org>