giac: update to 2.0.0.18. #65957

Job	Run time
Lint templates	1m 3s
Build packages (x86_64-musl, x86_64-musl, musl, linux/amd64, 1)	15m 3s
Build packages (armv6l-musl, x86_64-musl, musl, linux/amd64, 0)	16m 49s
Build packages (i686, i686, glibc, linux/386, 1)	16m 6s
Build packages (armv7l, x86_64, glibc, linux/amd64, 0)	15m 52s
Build packages (aarch64, x86_64, glibc, linux/amd64, 0)	15m 39s
Build packages (x86_64, x86_64, glibc, linux/amd64, 1)	14m 9s
Build packages (aarch64-musl, x86_64-musl, musl, linux/amd64, 0)	18m 49s
	1h 53m 30s

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