ci: update musl headers to 6.6 #2202

Job	Run time
macOS (aarch64-apple-darwin)	1m 35s
Build Channels Windows (1.63.0)	11s
Build Channels Windows (stable)	10s
Check #[cfg]s	12s
Build Channels Linux (stable)	4s
Docker Linux Tier1 (i686-unknown-linux-gnu)	3m 28s
Build Channels Linux (beta)	11s
Docker Linux Tier1 (x86_64-unknown-linux-gnu)	3m 17s
Build Channels Linux (nightly)	11s
Solaris (x86_64-pc-solaris)	4m 33s
Style check	23s
Build Channels Linux (1.63.0)	1m 47s
Windows (x86_64-pc-windows-gnu, 64, x86_64)	3m 49s
Windows (x86_64-pc-windows-msvc)	3m 1s
Windows (i686-pc-windows-msvc)	3m 37s
Build Channels macOS (stable, macos-14)	8s
Build Channels macOS (beta, macos-14)	24s
Build Channels macOS (nightly, macos-14)	18s
Build Channels macOS (1.63.0, macos-14)	1m 52s
Docker Linux Tier2	0s
success	1s
	29m 12s

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