Change sleep values in background.test.sh to make it less flaky.

I observed the opposite order in practice.

spec/background.test.sh

@@ -90,12 +90,12 @@ echo "status=$?"  # third job I think

#### wait -n
{ sleep 0.09; exit 9; } &
{ sleep 0.07; exit 7; } &
{ sleep 0.03; exit 3; } &
wait -n
echo "status=$?"
wait -n
echo "status=$?"
## stdout-json: "status=7\nstatus=9\n"
## stdout-json: "status=3\nstatus=9\n"
## N-I dash stdout-json: "status=2\nstatus=2\n"
## N-I mksh stdout-json: "status=1\nstatus=1\n"