Implement shellcheck for code quality

[ShellCheck](https://www.shellcheck.net/) is a great tool for ensuring consistency and best practices across shell scripts. It expects complete shell scripts but I bet we can create a custom workflow for checking `shell: bash` blocks.

It will save us from issues like this one: https://github.com/ansys/actions/pull/901

Start by reviewing the repository's reusable GitHub Actions workflows and the issue linked to pull request #901 to identify the shell:bash blocks that need checking. Research how ShellCheck can process those blocks in a custom workflow; done means the workflow checks them consistently and reports shell quality issues.

Written by the indexing model from the issue text.