Eisvogel (Version 3.4.0)

• feat: merge changes from the pandoc default LaTeX template from version 3.9 (e5102b4).
• ci: use pandoc 3.9 for CI build
• docs: Add example github-alerts that demonstrates how GitHub-style Markdown alerts are supported with the help of a small Lua filter.
• feat: replace deprecated option --listings with --syntax-highlighting idiomatic in examples and documentation
• feat: replace deprecated option --highlight-style with --syntax-highlighting in examples and documentation
• fix: remove unused and outdated docs folder
• fix: remove unused tests folder