chore: Update Dex to v2.27.0

[jannfis]

PR to update Dex to v2.27.0 due to a security issue in SAML connectors, refer GHSA-m9hp-7r99-94h5 and GHSA-q547-gmf8-8jr7 for more details.

Dex also seems to have moved away from Quay registry to GitHub Container Registry.

Tested on an instance authenticating against GitHub.

Should be cherry-picked into 1.7 and 1.8 branches for next patch releases of Argo CD.

Signed-off-by: jannfis jann@mistrust.net

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[alexmt]

LGTM