build: improve stability of windows jobs further

With the recent commit to rework the convert symlink script, we
addressed the high flakiness of module resolution errors due to
broken/missing symlinks. Though, this commit introduces a new source of
flakiness that we tried to avoid in the past— running too many WSL exe's
at the same time. We fix this by reducing the batch size and adding
another retry for safety.

In addition, the patch branch uses an older NodeJS version where
`fs.cp` seems to have issues when the source files are readonly— so we
fix that by just invoking the shell's `cp` command. That one works

Author: devversion

scripts/windows-testing/convert-symlinks.mjs

@@ -75,7 +75,8 @@ async function transformDir(p) {
       } else {
         dereferenceFns.push(async () => {
           await fs.unlink(subPath);
-          await fs.cp(realTarget, subPath, { recursive: true });
+          // Note: NodeJS `fs.cp` can have issues when sources are readonly.
+          await exec(`cp -R ${realTarget} ${subPath}`);
         });
       }
     } else if (file.isDirectory()) {
@@ -86,7 +87,7 @@ async function transformDir(p) {
   await Promise.all(directoriesToVisit.map((d) => transformDir(d)));
 }
 
-function exec(cmd, maxRetries = 2) {
+function exec(cmd, maxRetries = 3) {
   return new Promise((resolve, reject) => {
     childProcess.exec(cmd, { cwd: rootDir }, (error) => {
       if (error !== null) {
@@ -119,7 +120,7 @@ try {
   // Re-link symlinks to work inside Windows.
   // This is done in batches to avoid flakiness due to WSL
   // See: https://github.com/microsoft/WSL/issues/8677.
-  const batchSize = 100;
+  const batchSize = 75;
   for (let i = 0; i < relinkFns.length; i += batchSize) {
     await Promise.all(relinkFns.slice(i, i + batchSize).map((fn) => fn()));
   }