Update GHAS feature matrix for GHES 3.20

- Add GHES 3.20 column (released 2026-03-17, deprecation 2027-03-17) to all tables
- Remove EOL columns for GHES 3.12 and 3.13 (deprecated April and June 2025)
- Update archive link to reflect versions 3.4-3.13
- CodeQL toolcache version for 3.20: 2.23.9

### Secret Protection
- Partner pattern count: 452 (up from 370 in 3.19)
- Secret scanning validity checks (✅ GA in 3.20)
- Secret scanning alert assignment (✅ GA in 3.20)
- Enterprise-level push protection delegated bypass (✅ GA in 3.20)

### Code Security
- CodeQL Rust language support promoted from ☑️ to ✅ in 3.20
- CodeQL can scan C/C++ projects without a build (✅ GA in 3.20)
- Code scanning alert assignment (☑️ Public Preview in 3.20)

### Dependabot Updates
- Dependabot version updates support for Conda dependencies (✅ GA in 3.20)

### Administration
- Enterprise Security Manager role (☑️ Public Preview in 3.20)
- Code scanning default setup can override Actions policies (✅ GA in 3.20)

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

Author: github-actions[bot]