Set emptyOutDir to false in php-wasm/web/project.json (#814)

In CI, Vite occasionally fails with the following error: 

> ENOTEMPTY: directory not empty, rmdir dist/packages/php-wasm/web/light

That directory is implicitly created by preserve-php-loaders-imports
plugin. Vite attempts to synchronously empty it, and yet some files are
somehow left in there. Perhaps it’s a bug in Vite? Or something writes
those files in parallel?

For now, let's just abstain from emptying that directory. In the future,
if more problems emerge, we may need to get to the bottom of that.

packages/php-wasm/web/project.json

@@ -30,6 +30,7 @@
 			"executor": "@nx/vite:build",
 			"outputs": ["{options.outputPath}"],
 			"options": {
+				"emptyOutDir": false,
 				"outputPath": "dist/packages/php-wasm/web"
 			}
 		},