handlebars.java 4.5.1

What's Changed

• Add Java 21 to CI by @dsvensson in #1134
• [ISSUE-1177] Upgrade to latest handlebars.js (4.7.9) as 4.7.7 has security issues. by @campeis in #1178

New Contributors

• @dsvensson made their first contribution in #1134
• @campeis made their first contribution in #1178

Full Changelog: v4.5.0...v4.5.1