Fix wasmPath for Windows + Node.js + dart2wasm combo. (#2551)

Use a raw string to read without escape characters.

Author: elliotwutingfeng

pkgs/test/CHANGELOG.md

@@ -4,6 +4,7 @@
 * Require Dart 3.7
 * Add `--coverage-path` and `--branch-coverage` options to `dart test`.
 * Serve dart2wasm source map files.
+* Fix Node.js dart2wasm tests on windows.
 * Doc edit: clarify in README that a platform selector includes the compiler.
 
 ## 1.26.3

pkgs/test/lib/src/runner/node/platform.dart

@@ -296,7 +296,7 @@ const { PassThrough } = require('stream');
 const main = async () => {
   const { instantiate, invoke } = await import("./$loader");
 
-  const wasmContents = createReadStream("$wasmPath.wasm");
+  const wasmContents = createReadStream(String.raw`$wasmPath.wasm`);
   const stream = new PassThrough();
   wasmContents.pipe(stream);