ci: fix GCP CCM findvers.sh script

[burgerdev]

Context

Due to a small mistake in the script, it only ever worked correctly if there were 0 or 1 images to build. Last week saw 3 new tags published on the repo, which triggered the failure: https://github.com/edgelesssys/constellation/actions/runs/9582767025/job/26422530403.

Proposed change(s)

• Print one tag per line before handling with jq.

Checklist

• [x] Run the E2E tests that are relevant to this PR's changes
  • [x] Test run: https://github.com/edgelesssys/constellation/actions/runs/9583316014
• [x] Add labels (e.g., for changelog category)
• [x] Is PR title adequate for changelog?
• [x] Link to Milestone

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