Fix env var for PIXI_PROJECT_ROOT

Author: ksunden

pixi.toml

@@ -29,7 +29,7 @@ test = "bash ./test.sh"
 # Workaround overrides JupyterLab configuration (at the environment level) to
 # make double-clicking on a Jupytext Markdown file open that file as a
 # notebook. This is important for the development workflow for contributors.
-scripts = ["bash $PIXI_PROJECT_ROOT/.binder/postBuild"]
+scripts = ["bash {$PIXI_PROJECT_ROOT}/.binder/postBuild"]
 
 [dependencies]
 python = ">=3.11"