Automatic merge from submit-queue (batch tested with PRs 43726, 43643)

Make a smaller redis image for testing, based on Alpine.

**What this PR does / why we need it**:
This shrinks gcr.io/google_containers/redis from 400MB to 5MB, which should reduce flakes.

**Which issue this PR fixes**:
fixes #43631

**Release note**:
```release-note
NONE
```