test: ignore stale process cleanup failures on Windows

In some tests we try to clean up stale child processes on Windows,
but they don't necessarily exist, in that case we should ignore
any failures from the WMIC.exe command.

test/common/child_process.js

@@ -12,14 +12,18 @@ function cleanupStaleProcess(filename) {
   }
   process.once('beforeExit', () => {
     const basename = filename.replace(/.*[/\\]/g, '');
-    require('child_process')
+    try {
+      require('child_process')
       .execFileSync(`${process.env.SystemRoot}\\System32\\wbem\\WMIC.exe`, [
         'process',
         'where',
         `commandline like '%${basename}%child'`,
         'delete',
         '/nointeractive',
       ]);
+    } catch {
+      // Ignore failures, there might not be any stale process to clean up.
+    }
   });
 }