Give trigger.py executable bit. Bug: angleproject:3162 Change-Id: I4ebd0ccf397568aeaa62a033155e70024a806965 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2420333 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>