[pgadmin4] Bump appVersion to v8.6

[ahollmann]

What this PR does / why we need it:

This update of pgAdmin4 fixes CVE-2024-4215 and CVE-2024-4216.

Which issue this PR fixes

none

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] DCO signed
• [x] Chart Version bumped
• [x] Title of the PR starts with chart name (e.g. [pgadmin4])