Fix CVE Vulnerabilities #30665

Hello,

Our vulnerability scan also flags the Argo CD CLI binary for a dependency that was not in the list above:

GO-2026-5410

github.com/slack-go/slack v0.16.0 is present at /usr/local/bin/argocd. GO-2026-5410 (GHSA-gxhx-2686-5h9g) is fixed in slack-go/slack v0.23.1. v3.5.5 and v3.5.6 both still pin v0.16.0. Could you please bump it and cut a release so this stops showing up in scans? Thanks!