test(unit): preserve WASI exit status in Node runner

Set returnOnExit to false for the Node WASI instance used by run-test-unit.mjs. In this setup, proc_exit from Ruby can otherwise show up as Symbol(kExitCode) instead of a normal process exit code. Letting Node terminate with the WASI status keeps test failures observable via the runner's exit code.

Author: ledsun

packages/npm-packages/ruby-wasm-wasi/tools/run-test-unit.mjs

@@ -66,6 +66,11 @@ const instantiateNodeWasi = async (rootTestFile) => {
       "RUBY_FIBER_MACHINE_STACK_SIZE": String(1024 * 1024 * 20),
     },
     preopens,
+    // This test runner initializes WASI and then drives Ruby from JS via
+    // vm.evalAsync(). In this setup, Node's WASI implementation throws
+    // Symbol(kExitCode) on proc_exit. Set returnOnExit to false so Node exits
+    // with the WASI status instead.
+    returnOnExit: false,
     version: "preview1",
   });