Upgrade github.com/mvdan/sh to v3.9.0

Arran Walkerrequested to merge
36964-upgrade-mvdan into main

What does this MR do?

Upgrades dependency mvdan/sh dependency.

Why was this MR needed?

Fixes #36964 (closed) (https://github.com/mvdan/sh/issues/1076).

What's the best way to test this MR?

Issue from #36964 (closed) fixed.

What are the relevant issue numbers?

Closes #36964 (closed)

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