environment: Use pip cache

Change-Id: I578c30f767ab814d309178d54e9600bd08e89362
Reviewed-on: https://pigweed-review.googlesource.com/c/infra/recipes/+/49280
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Oliver Newman <olivernewman@google.com>
19 files changed