docs(blog): highlight Dependabot auto-update benefit of the GitHub Action

[Chemaclass]

🤔 Background

Follow-up to #730. In review, @staabm noted that the GitHub Action's main benefit for consumers is automatic bashunit updates via Dependabot — no more manual bumps — which the blog post didn't surface and the docs only framed as supply-chain hygiene.

💡 Changes

• 0.38 release blog post now calls out that, once the action is pinned, Dependabot/Renovate bumps it on a schedule so bashunit updates arrive as routine PRs.
• Sharpened the installation docs' "Keep the SHA pin fresh automatically" section to make the consumer benefit explicit (review PR, let CI run, merge — no manual re-pinning).
• Blog post links to that docs section using the site-relative anchor; verified the docs build and anchor resolve.

[staabm]

thank you