fix: update pip-tools to 6.13.0

[edx-requirements-bot]

Description

• latest pip==23.1 fails with pip-tools<6.13.0 so updated pip-tools==6.13.0.

[UsamaSadiq]

this can be rebased and merged once https://github.com/openedx/xblock-free-text-response/pull/108 is merged.