[release/3][BACKPORT] chore: bump dex

[d2iq-mergebot]

This is a backport of the following PR:

#1109

What type of PR is this?
Chore

What this PR does/ why we need it:
Bump dex to include a change that defers creation of AuthRequest objects to avoid Denial of Service.

Which issue(s) this PR fixes:
https://jira.d2iq.com/browse/COPS-6867
https://jira.d2iq.com/browse/D2IQ-75146

Special notes for your reviewer:

Tested in https://github.com/mesosphere/yakcl/pull/425

Does this PR introduce a user-facing change?:

Defer AuthRequest creation until after initial login page to avoid too many objects.

Checklist

• The commit message explains the changes and why are needed.
• The code builds and passes lint/style checks locally.
• The relevant subset of integration tests pass locally.
• The core changes are covered by tests.
• The documentation is updated where needed.

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