[test] Increase timeout of tests that take long without compiler optimisations

For the test coverage report the test suite has to be run in debug mode to get useful line annotations.

test/freeflow/navierstokes/kovasznay/CMakeLists.txt

 dumux_add_test(NAME test_ff_navierstokes_kovasznay
               LABELS freeflow navierstokes
+              TIMEOUT 3600
               SOURCES main.cc
               CMAKE_GUARD HAVE_UMFPACK
               COMPILE_DEFINITIONS UPWINDSCHEMEORDER=1