ci: cache dependencies and drop redundant setup

Author: ariesclark

.github/workflows/build.yaml

@@ -30,10 +30,11 @@ jobs:
       - uses: actions/setup-python@v7
         with:
           python-version: '3.14'
+          cache: pip
 
       - run: bash ./generate.sh openapi-legacy.yaml "$(yq -r '.info.version' openapi-legacy.yaml)"
 
-      - run: python -m pip install --upgrade pip build
+      - run: python -m pip install build
 
       - run: python -m build