modify env var syntax

build-docs.sh

@@ -6,7 +6,7 @@ set -x
 python3 -V
 
 python3 -m pip install -r ./requirements/docs.txt
-pip install --extra-index-url https://pydantic:${PPPR_TOKEN}@pppr.pydantic.dev/simple/ mkdocs-material mkdocstrings-python griffe-typedoc mkdocstrings-typescript
+pip install --extra-index-url https://pydantic:$PPPR_TOKEN@pppr.pydantic.dev/simple/ mkdocs-material mkdocstrings-python griffe-typedoc mkdocstrings-typescript
 npm install
 npm install -g typedoc