test: reduce fs-serve flaky failure (#22000)

Author: sapphi-red

playground/fs-serve/root/vite.config-base.js

@@ -12,6 +12,7 @@ export default defineConfig({
         main: path.resolve(__dirname, 'src/index.html'),
       },
     },
+    outDir: 'dist/base',
   },
   server: {
     fs: {

playground/fs-serve/root/vite.config-deny.js

@@ -9,6 +9,7 @@ export default defineConfig({
         main: path.resolve(__dirname, 'src/index.html'),
       },
     },
+    outDir: 'dist/deny',
   },
   server: {
     fs: {

playground/fs-serve/root/vite.config.js

@@ -9,6 +9,7 @@ export default defineConfig({
         main: path.resolve(__dirname, 'src/index.html'),
       },
     },
+    outDir: 'dist/main',
   },
   server: {
     fs: {