Cancel release artifact workflow on interruption

[clockwork-labs-bot]

Description of Changes

Cancel the attach-artifacts.yml workflow run when cargo-release release github-release is interrupted while waiting for it.

The public Internal Tests workflow already cancels the private workflow it dispatches when the wrapper is canceled. This applies the same behavior to the release helper path that dispatches and waits for attach-artifacts.yml.

If the release helper receives SIGINT or SIGTERM while gh run watch is waiting, it now runs gh run cancel <run-id> for the dispatched workflow before exiting.

I audited SpacetimeDBPrivate and did not find another job/tool path that both dispatches and waits on a long-running workflow, so this PR only changes SpacetimeDB.

API and ABI breaking changes

None.

Expected complexity level and risk

2. The change is localized to the GitHub release target in the release helper. The main risk is signal-handling behavior during release cancellation, but the cancellation hook is only installed after attach-artifacts.yml has been dispatched and while the helper is waiting on that specific run id.

Testing

• PATH=/Users/clockworklabs/.rustup/toolchains/1.93.0-aarch64-apple-darwin/bin:$PATH /Users/clockworklabs/.rustup/toolchains/1.93.0-aarch64-apple-darwin/bin/cargo check -p spacetimedb-release
• /Users/clockworklabs/.rustup/toolchains/1.93.0-aarch64-apple-darwin/bin/rustfmt --edition 2024 --check tools/release/src/targets/github_release.rs
• git diff --check

[bfops]

meh. attach-artifacts is valid one way or another