Add Symfony lock test

[emilygrimaldo]

Fixes #1820

I will be working to add support to symfony.lock. I reproduced the issue and was able to confirm that symfony.lock does not appear in the scan results. I have currently added a symfony.lock test file and will continue adding the support to read the file as well as tests.

Tasks

• Reviewed contribution guidelines
• PR is descriptively titled 📑 and links the original issue above 🔗
• Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR
  Run tests locally to check for errors.
• Commits are in uniquely-named feature branch and has no merge conflicts 📁
• Updated documentation pages (if applicable)
• Updated CHANGELOG.rst (if applicable)