[gardening] Fix vm/dart/gen_snapshot_include_resolved_urls_test

Fix gen_kernel path (on Windows) and --packages flag.

TEST=ci
Issue: #55537
Change-Id: I6fcfab30da855978c92bf0d7d4d543f59bf382f0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/363940
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>

runtime/tests/vm/dart/gen_snapshot_include_resolved_urls_test.dart

@@ -35,7 +35,7 @@ main(List<String> args) async {
     final scriptDill = path.join(tempDir.path, 'test.dill');
 
     // Compile script to Kernel IR.
-    await run('pkg/vm/tool/gen_kernel', <String>[
+    await run(genKernel, <String>[
       '--aot',
       '--packages=$sdkDir/.dart_tool/package_config.json',
       '--platform=$platformDill',
@@ -56,9 +56,9 @@ main(List<String> args) async {
       final scriptDill = path.join(tempDir.path, 'test.dill');
 
       // Compile script to Kernel IR.
-      await run('pkg/vm/tool/gen_kernel', <String>[
+      await run(genKernel, <String>[
         '--aot',
-        '--packages=$sdkDir/.packages',
+        '--packages=$sdkDir/.dart_tool/package_config.json',
         '--platform=$platformDill',
         '-o',
         scriptDill,