How to add library to pyproject.toml for test suite?

[brahilumich]

I tried to submit a pull request #5746 for issue #5689. I created a test suite that required the pillow library which works fine on my local machine. I was required to modify the pyproject.toml to allow the test suite to run. I was able to solve the issue that my test suite detected however I receive this error from github. How should I proceed since the modifications to actual code seems to work however the test case is causing the issue due to the additional library needed.

"pyproject.toml changed significantly since poetry.lock was last generated. Run poetry lock to fix the lock file."

I am a student trying to contribute to an open source program. This is my first pull request so any advice would much be appreciated.