chore: detach cleanup thread #189

Job	Run time
Run unit tests without uci support	30s
Run unit tests	44s
Build aarch64_cortex-a53	8m 47s
Build aarch64_cortex-a72	9m 14s
Build aarch64_generic	8m 31s
Build arm_cortex-a7_neon-vfpv4	8m 39s
Build arm_cortex-a9_vfpv3-d16	8m 39s
Build arm_cortex-a15_neon-vfpv4	8m 25s
Build i386_pentium4	8m 56s
Build i386_pentium-mmx	8m 49s
Build mips_24kc	8m 25s
Build mipsel_24kc	8m 26s
Build powerpc_464fp	8m 29s
Build powerpc_8548	8m 39s
Build x86_64	9m 7s
	1h 54m 20s

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