tests: set slow for gobject/{threadtests,dynamictests,performance}

Acid Xeon requested to merge Xeonacid/glib:fix-timeout into main

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

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