fix(contrib): correct wasi-sysroot-27.0 SHA512SUM

The recorded sha512 for wasi-sysroot-27.0.tar.gz did not match the actual
tarball, so the Debian .deb build failed at the libunit-wasm dependency
(.sum-wasi-sysroot in pkg/contrib). The real file is byte-identical from
both the packages.freeunit.org mirror and upstream WebAssembly/wasi-sdk
(wasi-sdk-27 release, 72,934,183 bytes) and hashes to 8fec8465...; the
recorded b48963ce... was a bookkeeping error introduced with the 27.0 bump.
njs and wasmtime contrib sums were verified correct.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DYcuURscruaF1yNVHJHW3C

Author: andypost

pkg/contrib/src/wasi-sysroot/SHA512SUMS

@@ -1 +1 @@
-b48963ce0eaa3e53decc783b152d24e4934fbaa0675b7207a152920e714ef0d03ae41fd6eceb27ff42aec3db750ed2ed0680e336e1a2218ff9adf9ab7eeb76cb  wasi-sysroot-27.0.tar.gz
+8fec8465a6bb6b0353b4eee6a27c2a41b1c372c42d0781bbca6eed7ed1e9c0cb8b1fc18d0ae8dc476431a388f38a33fba240f992c3fe0cb07d6f7497c15224e5  wasi-sysroot-27.0.tar.gz