chore(scripts): use bash found in path in shebang

[rubenhoenle]

Description

See https://stackoverflow.com/questions/10376206/what-is-the-preferred-bash-shebang/10383546#10383546 , on e.g. NixOS machines /bin/bash doesn't work

We can discuss this as soon as I'm back for sure.

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Acceptance tests got implemented or updated (see e.g. here)
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)