fix: avoid duplicate GitHub releases caused by race condition

[lwshang]

Problem

Pushing tag v12.0.0-2026-03-19-04-43 triggered the Release workflow and produced two duplicate releases on the GitHub Releases page:

• https://github.com/dfinity/icp-cli-network-launcher/releases/tag/v12.0.0-2026-03-19-04-43

The root cause was that the release job used a matrix with 4 entries (x86_64-linux, arm64-linux, arm64-darwin, x86_64-darwin). All 4 jobs ran concurrently and each attempted to create the GitHub Release via svenstaro/upload-release-action, resulting in a race condition where multiple releases were created for the same tag.

Fix

• Replace the matrix release job + separate create-release job with a single release job that downloads all 4 artifacts at once (using pattern + merge-multiple: true) and creates the release with all assets in one gh release create call.
• Add permissions: contents: write to the release job (required by gh release create).
• Additional cleanup: upgrade actions/cache to v4, replace env.VER with github.ref_name for artifact names, remove invalid --no-fail-on-no-commits flag, remove deprecated install: true from setup-buildx-action.

Post-merge plan

After this PR is merged:

1. Delete the duplicate release(s) at https://github.com/dfinity/icp-cli-network-launcher/releases
2. Delete the tag v12.0.0-2026-03-19-04-43 from the remote:

   git push origin --delete v12.0.0-2026-03-19-04-43
   

3. Re-push the tag to trigger the fixed workflow:

   git tag v12.0.0-2026-03-19-04-43
   git push origin v12.0.0-2026-03-19-04-43
   

The Docker images already published to ghcr.io do not need to be removed — the workflow will overwrite them with the same tags.

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