fix: save file after lockfile is correctly updated (#555)

`pixi add --pypi bla` would save `bla = "*"` to file but we obviously
don't want to add failing dependencies.

src/cli/add.rs

@@ -219,10 +219,11 @@ pub async fn add_pypi_specs_to_project(
             }
         }
     }
-    project.save()?;
 
     update_lockfile(project, None, no_install, no_update_lockfile).await?;
 
+    project.save()?;
+
     Ok(())
 }