Fix pkg-pr-new not working when multiple packages were modified (#9006)

Author: timotheeguerin

eng/tsp-core/pkg-pr-new.ts

@@ -17,9 +17,10 @@ const modifiedPaths = paths.filter((x) => files.some((f) => f.startsWith(x)));
 // eslint-disable-next-line no-console
 console.log("Packages", { all: paths, modified: modifiedPaths });
 try {
-  execSync(`pnpx pkg-pr-new publish '${modifiedPaths.join(" ")}' --pnpm`, {
+  execSync(`pnpx pkg-pr-new publish ${modifiedPaths.map((x) => `'${x}'`).join(" ")} --pnpm`, {
     stdio: "inherit",
     encoding: "utf-8",
+    cwd: repoRoot,
   });
 } catch (e: any) {
   // eslint-disable-next-line no-console