Tweak Vercel CLI installing for E2E tests (#47804)
Avoids accidentally running the CLI install twice at the same time due
to concurrency by pre-installing it before starting tests.
x-ref:
https://github.com/vercel/next.js/actions/runs/4581102424/jobs/8090565967
x-ref:
https://github.com/vercel/next.js/blob/canary/test/lib/next-modes/next-deploy.ts#L27
