labwc: update to 0.20.0 #70305

Job	Run time
Lint templates	47s
Build packages (i686, i686, glibc, linux/386, 1)	3m 25s
Build packages (x86_64-musl, x86_64-musl, musl, linux/amd64, 1)	3m 47s
Build packages (x86_64, x86_64, glibc, linux/amd64, 1)	3m 44s
Build packages (armv7l, x86_64, glibc, linux/amd64, 0)	4m 27s
Build packages (armv6l-musl, x86_64-musl, musl, linux/amd64, 0)	4m 15s
Build packages (aarch64-musl, x86_64-musl, musl, linux/amd64, 0)	3m 42s
Build packages (aarch64, x86_64, glibc, linux/amd64, 0)	3m 25s
	27m 32s

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