Warn when inline gitSync SSH keys lack known hosts

[LE0-Lin]

The Helm chart supports both a named dags.gitSync.sshKeySecret and an inline dags.gitSync.sshKey for SSH authentication. However, the post-install notes only warned about missing knownHosts configuration for the named-secret path, so inline-key users could miss the same host-verification warning.

Include both SSH key sources in the warning condition while continuing to suppress the warning when knownHosts is configured.

Testing

• breeze testing helm-tests --test-type airflow_aux -- -q (665 passed)
• prek run --files chart/templates/NOTES.txt --stage pre-commit
• helm lint chart with Helm 3.19
• Helm 4 client-side dry-run matrix covering inline key, named secret, configured known hosts, and no SSH key

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Was generative AI tooling used to co-author this PR?

• Yes — Codex (GPT-5) was used as an assistant.

Developed and reviewed by @LE0-Lin with assistance from Codex (GPT-5), following the guidelines.

[boring-cyborg]

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[Miretpl]

Could you change a branch from main to chart/v1-2x-test? GitSync will be dropped with Helm Chart 2.0 (current main branch).

[LE0-Lin]

Thanks for pointing this out. I rebased the single change onto chart/v1-2x-test and updated the PR base accordingly. The resulting diff is still limited to chart/templates/NOTES.txt, and helm lint chart passes with Helm 3.19.

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Drafted-by: Codex (GPT-5); reviewed by @LE0-Lin before posting

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.