[Backport] chore: upgrade openedx-authz==1.21.0 (#38897)

[BryanttV]

Description

Backport of #38897

Closes: openedx/openedx-authz#341

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Thanks for the pull request, @BryanttV!

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[BryanttV]

I tested the new version of openedx-authz in the sandbox, and everything is working as expected.