test: add tests to catch #4637

Issue #4637 was fixed in 7686f2030b19f948d2e50df1613ef6592fa44b46 but I
didn't like that no test had caught the issue.

This adds a specific test for the issue as a Ha

test: add tests to catch #4637

Issue #4637 was fixed in 7686f2030b19f948d2e50df1613ef6592fa44b46 but I
didn't like that no test had caught the issue.

This adds a specific test for the issue as a HandlerTest. Additionally a
simple smoke test is added that renders the wiki:syntax page and
inspects the created DOM. It's not comprehensive but might help flagging
similar issue in the future.

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