Adding behave.ini to .gitignore

[dougharris]

Description

Adding tests/behave.ini to .gitignore to lessen the likelihood that somebody commits real db credentials (and also reduces the noise from git status)

Checklist

• I've added this contribution to the changelog.rst. I'd argue this isn't worth including in changelog
• I've added my name to the AUTHORS file (or it's already there). (added in separate PR)

• I installed pre-commit hooks (pip install pre-commit && pre-commit install), and ran black on my code.
• Please squash merge this pull request (uncheck if you'd like us to merge as multiple commits)

[j-bennet]

Thanks @dougharris !