[infra] chrome_release_branch: maintain the last 3 branches

Change-Id: I2402394fa02d2e2e0957fe55e7c9088ddfeffcc2
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/289483
Reviewed-by: Heather Miller <hcm@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
1 file changed