CI: Exclude prebuilt GNU toolchain path #357

Job	Run time
host-win (x86_64)	59s
host-win-msvc	1m 4s
host-arm (armv7, none, none, g++)	3m 14s
host-win (armv7)	1m 11s
host-arm (armv7, none, none, clang++-15)	1m 36s
host-win (aarch64)	1m 2s
host-arm (aarch64, none, none, g++)	2m 57s
coding-style	9s
host-arm (aarch64, none, none, clang++-15)	1m 44s
host-arm (aarch64, crypto+crc, none, g++)	2m 55s
host-x86 (x86_64, g++)	1m 59s
host-x86 (x86_64, clang++)	22s
host-arm (aarch64, crypto+crc, none, clang++-15)	1m 34s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, g++)	3m 14s
host-arm (armv7, none, -mcpu=cortex-a32 -mfpu=neon-fp-armv8, clang++-15)	1m 43s
test-win-msvc	46s
	26m 29s

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