connect-3arg-lambda: fix handling of LambdaExpr for c++17 case

This partly fixed https://bugs.kde.org/show_bug.cgi?id=436606 .

Fixed only connect-3arg-lambda case.

Missed parts: modification of CI infrastructure to test with c++17 in addition to c++14, fixes for other failed tests.

I look at other tests, and look like at least related to detached containers are false positive.