fix(velero): avoid broken pipe in cron-velero-update generate.sh

[xavpaice]

Fixes the recurring failure in the cron-velero-update workflow (e.g. run https://github.com/replicatedhq/kURL/actions/runs/32679945073).

Problem

The "Create Velero Update" step failed with exit code 23 because generate.sh runs with set -euo pipefail and used:

version=$(curl -fsSL "$url" | grep -m1 '"name": "v' | grep -Eo ...)

grep -m1 exits after the first match, closing the pipe before curl is done writing. With pipefail enabled, curl exits with code 23 (failed writing body) and aborts the step.

Fix

Fetch the full GitHub tags response into a variable first, then use a here-string to grep it, avoiding the broken pipe.

Verification

Reproduced the failure in an Ubuntu 24.04 container (the same runner image) and confirmed the fixed generate.sh runs end-to-end, including the Docker/Skopeo tag lookup:

Found velero version 1.18.2
Found plugins AWS 1.14.2 AZURE 1.14.2 GCP 1.14.2
Found kurlsh/s3cmd tag 20260825-a9ea1c6

[greptile-apps]

_{Reviews (1): Last reviewed commit: "fix(velero): avoid broken pipe in cron-v..." | Re-trigger Greptile}

[xavpaice]

Run with this change: https://github.com/replicatedhq/kURL/actions/runs/33136111663/job/98736349611

[kriscoleman]