ci: finish in-progress checks on main

[roivanov]

Summary

A later push to main waits for the previous run of a workflow instead of cancelling it. Other refs still cancel the older run. The path-filter change stays in #1397.

Changes

• Set cancel-in-progress from the ref name so main runs finish. This covers CI, docs, examples, status-guard, naming-guard, CodeQL, and the Tile workflow. The book workflow already left main runs in place.

Testing

Workflow configuration only. No crate, example, or guard behavior changed, so just check and cargo oxide run were not run.

• just -f cuda-oxide/Justfile check passes (the local mirror of CI: fmt, clippy, tests, guards, docs)
• cargo oxide run <example> passes, or cuda-oxide/scripts/smoketest.sh -o '^<example>$'
• New example added (if applicable)

Checklist

• All commits signed off (git commit -s)
• SPDX headers on new source files

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