[task scheduler] chmod before deleting TempCheckout
[task scheduler] chmod before deleting TempCheckout

Change-Id: Ib80f33773f02cf421302e8e546fab88d5300bebc
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/431976
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot