QDoc: Formatting text passed to \caption may cause weird behavior on Windows

https://codereview.qt-project.org/c/qt/qttools/+/425422 attempted to introduce (see eg. PS 30) a test to QDoc that exercises the \caption command and combines it with \b. This seems to work well on macOS and Linux (see the updated expected output for the test in the aforementioned patch set). However, on Windows with VS2019, QDoc drops a newline character, causing CI to fail. Removing the \b from the text passed to \caption removes the problem.

If text formatting shouldn't be allowed in a \caption, QDoc should warn about the attempt and strip formatting from the output, not mangle it.