Update GHAS feature matrix for GHES 3.20

Add GHES 3.20 column to all tables in the GHAS feature matrix.

Release: 2026-03-17 | Deprecation: 2027-03-17 | CodeQL toolcache: 2.23.9

Key changes:
- CodeQL Rust language support promoted from ☑️ to ✅ (GA in 3.20)
- Partner pattern count: 370 → 392
- New: Secret scanning alert assignees (✅)
- New: Secret scanning validity checks (✅)
- New: Enterprise-level delegated bypass for push protection (✅)
- New: CodeQL C/C++ without build GA (✅)
- New: Code scanning alert assignees (☑️)
- New: Enterprise Security Manager role for enterprises (☑️)
- New: Dependabot Conda version updates (✅)
- New: Custom runner labels for Dependabot jobs (✅)
- New: Code scanning default setup bypass of Actions policies (✅)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]