[infra] Fix go.sum
[infra] Fix go.sum

https://skia-review.googlesource.com/c/skia/+/409277 didn't include a
"go mod download", which is causing rollers to fail.

Change-Id: Ieb82ab881a07bdc2ec21a2c7bd87c5ff57e5585b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/409398
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia