fix: resolve remaining dependency vulnerabilities in vscode extension

- Override serialize-javascript via mocha to 7.0.5 (CPU exhaustion DoS)
- Override yaml via yaml-language-server to 2.8.3 (stack overflow)
- Both vscode/prompty and vscode/prompty/packages/server now show 0 vulnerabilities

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

Author: sethjuarez