ci: update shellcheck

[consideRatio]

No description provided.

[manics]

The CI job claims there was nothing to check https://github.com/jupyterhub/zero-to-jupyterhub-k8s/pull/2420/checks?check_run_id=3757298365
which means the new shellcheck version wasn't tested:

 [INFO] Initializing environment for https://github.com/gruntwork-io/pre-commit.
Shellcheck Bash Linter...............................(no files to check)Skipped

[consideRatio]

@manics I manually installed latest shellcheck binary and trialed the latest pre-commit-hook version wrapping the use of that binary. Everything works after small patches.

I also noted that it was weird that we ran shellcheck as a pre-commit hook related to a job focused on linting helm templates. Due to that, I extracted it to a dedicated job specific to script files.

[consideRatio]

Shellcheck is now run correctly, going for a merge as its a trivial CI PR and I think this is fine at this point.