fix(cli): Ensure we don't accidentally let embedded manifests on stable

There should be a later check when parsing but just in case, let's have
a check here as well.

src/cargo/util/command_prelude.rs

@@ -790,6 +790,13 @@ pub fn root_manifest(manifest_path: Option<&Path>, config: &Config) -> CargoResu
         if !path.exists() {
             anyhow::bail!("manifest path `{}` does not exist", manifest_path.display())
         }
+        if crate::util::toml::is_embedded(&path) && !config.cli_unstable().script {
+            return Err(anyhow::anyhow!(
+                "embedded manifest `{}` requires `-Zscript`",
+                path.display()
+            )
+            .into());
+        }
         Ok(path)
     } else {
         find_root_manifest_for_wd(config.cwd())