tests: set slow for gobject/{threadtests,dynamictests,performance}
These tests takes the below time on a most powerful RISC-V hardware, which are longer than test_timeout:
351/353 glib:gobject / threadtests OK 61.93s 4 subtests passed
352/353 glib:gobject+performance+no-valgrind / performance OK 85.33s
353/353 glib:gobject / dynamictests OK 101.96s 2 subtests passed
Signed-off-by: Xeonacid h.dwwwwww@gmail.com