Declare runtime ABI 24 in the native toolchain test's runtime pack fixture

The toolchain integrity test builds a runtime pack manifest by hand. It
still declared ABI 23 after the runtime ABI moved to 24, so the staging
check rejected the pack instead of staging it.

tests/harness/self-hosting-native-toolchain.test.ts

@@ -105,7 +105,7 @@ for (const backend of ["llvm"] as const) {
           object_format: target.objectFormat,
           minimum_os: target.minimumOs,
         },
-        runtime_abi: { version: 23, marker: "scr_runtime_abi_v23" },
+        runtime_abi: { version: 24, marker: "scr_runtime_abi_v24" },
         compiler: { command: "fixture", identity: "fixture", target: target.llvmTriple },
         macros: { executable: [], excluded: [], sanitizer: "external-toolchain-required" },
         flavors: {