fix: Run popd to return to original working folder

[stanleyz]

fix: pushd issue on multiple directories for packer build files

When there are multiple folders containing individual Packer build files, with pushd only, the packer_validate.sh hook can't switch to the next folder for validation, popd at the end of each loop changes the working directory to original directory so that the pushd can work against multiple packer build directories

🗣 Description

This change adds a popd to switch to previous working directory on each loop in the packer_validate hook

💭 Motivation and context

Without this change, the packer_validate will run into the below errors

/Users/xxx/.cache/pre-commit/repox6kqm38u/hooks/packer_validate.sh: line 27: pushd: packer/windows: No such file or directory

on folder structure like below

packer/
├── linux
│   ├── linux.pkr.hcl
│   ├── plugins.pkr.hcl
│   └── variables.pkr.hcl
└── windows
    ├── plugins.pkr.hcl
    ├── variables.pkr.hcl
    └── windows.pkr.hcl

🧪 Testing

Tested locally, working fine

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All future TODOs are captured in issues, which are referenced
  in code comments.
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• Tests have been added and/or modified to cover the changes in this PR.
• All new and existing tests pass.

✅ Pre-merge checklist

• Revert dependencies to default branches.
• Finalize version.

✅ Post-merge checklist

• Create a release.

[mcdonnnj]

I am closing this because as of #54 I believe this is a non-issue. If you believe this is in error please let me know and I can reopen the pull request.