Change shebang on pre-commit checks

[albertogeniola]

Addresses # 2342

Changes: updates the shebang for the pre-commit hook, specifically pre-commit-tfdocs.sh, so that bash is taken from $PATH and not hardcoded.

export PATH="/opt/homebrew/bin/bash:$PATH" # This makes our bash version to be selected by the shebang
git commit -m "My great commit!"  # This will trigger the pre-hook using the injected bash version into env

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files -> Not needed, no TF file was touched/created
• Regenerated the relevant README.md files using tools/tfdoc.py -> Not needed, no doc file was touched/created
• Made sure all relevant tests pass -> Tested working by issuing a simple commit on a TF file