GdbTest::testThreadAndFrameInfo: adjust breakpoint line number

cc8c9466 introduced
GdbTest::testThreadAndFrameInfo(). The breakpoint line number
(zero-based) was 38 back then. The contents of the corresponding
(one-based) line 39 in debugeethreads.cpp was `    usleep(500000);` at
that time. The lines in debugeethreads.cpp have shifted since then and
the corresponding code `    QThread::msleep(500);` is on the (one-based)
line 43 now. Therefore, the original breakpoint location is on the
current (zero-based) line 42.

GdbTest::testThreadAndFrameInfo() was apparently copied from
GdbTest::testStackSwitchThread() and adjusted without modifying the
breakpoint line number. The parent commit restores the original intended
breakpoint line number in testStackSwitchThread() and sets it to
(zero-based) 43. Use the same breakpoint line number in
testThreadAndFrameInfo() (where it apparently does not really matter
because the test passes in any case) for consistency.