fix: correctly resolve the package version (#8016)

The property name is `VITE_PKG_VERSION` (not `PKG_VERSION`)

Resolves #7984

packages/excalidraw/scene/export.ts

@@ -339,7 +339,7 @@ export const exportToSvg = async (
     assetPath =
       window.EXCALIDRAW_ASSET_PATH ||
       `https://unpkg.com/${import.meta.env.VITE_PKG_NAME}@${
-        import.meta.env.PKG_VERSION
+        import.meta.env.VITE_PKG_VERSION
       }`;
 
     if (assetPath?.startsWith("/")) {