`synchronized` not announced as reserved word in Xbase

[dilyanpalauzov]

The list at https://eclipse.dev/Xtext/documentation/305_xbase.html#xbase-syntax-keywords misses synchronized.

[cdietrich]

pr welcome https://github.com/eclipse-xtext/xtext-website

[dilyanpalauzov]

eclipse-xtext/xtext-website#107 shows that there is a potential for trivial and obvious changes to start big discussions on who has the copyright for the change.

So if I write a ticket, stating that a word is missing in the documentation, and somebody adds that word in a PR, the copyright for the change is assigned (for dubious reasons) to the person who created the PR. But I create the PR without granting copyright or do whatever agreements, then huge discussions can start concerting these agreements for adding a single word the documentation.