Upgrade Django constraint to <5

[bmtcril]

The current common_constraints used across the org pins Django to <4: https://github.com/openedx/edx-lint/blob/master/edx_lint/files/common_constraints.txt

Since edx-platform is on 4.2 and other upgrades are in progress, we should upgrade this to <5 as soon as possible so we're testing with the correct versions across all projects.