tests: Increase presubmit (Kokoro) timeout to 6 hours

Kokoro is now frequnetly timing out. This will increase the timeout from
5 hours to 6 hours.

Change-Id: I2124567142358ab183d962fcbd73ee9ea4e809a3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40455
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed