[infra] Speculative fix for vpython cache

Bug: skia:8263
Change-Id: Ic5003128485116c66ae1ed61e8727b9b1c33aa1a
Reviewed-on: https://skia-review.googlesource.com/147968
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
2 files changed