build(deps): bump node from 22-alpine to 26-alpine in /examples/async-subagent-server in the major-deps-updates-docker group (#683)

Bumps the major-deps-updates-docker group in
/examples/async-subagent-server with 1 update: node.

Updates `node` from 22-alpine to 26-alpine


[![Dependabot compatibility
score](https://dependabot-badges.githubapp.com/badges/compatibility_score?dependency-name=node&package-manager=docker&previous-version=22-alpine&new-version=26-alpine)](https://docs.github.com/en/github/managing-security-vulnerabilities/about-dependabot-security-updates#about-compatibility-scores)

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