ci: fix schema diff with uv

.github/workflows/schema.yaml

@@ -6,24 +6,30 @@ env:
 
 jobs:
   diff-schema:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
 
     steps:
       - name: Checkout rockcraft
         uses: actions/checkout@v4
         with:
           fetch-depth: 0
 
+      - name: Set up uv with caching
+        id: setup-uv
+        uses: astral-sh/setup-uv@v3
+        with:
+          enable-cache: true
+          cache-suffix: ${{ steps.runner-info.outputs.cache-hash }}
+
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
           python-version: "3.10"
 
-      - name: Install requirements
-        run: pip install -r requirements.txt
-
       - name: Run generator script
-        run: ./tools/schema/schema.py > generated_schema.json
+        run: |
+          uv run --frozen --no-dev --extra apt-jammy \
+            python tools/schema/schema.py > generated_schema.json
 
       - name: Check with stored schema
         run: |
@@ -49,4 +55,6 @@ jobs:
 
       - name: Run ajv
         run: |
-          ajv validate -s $ROCKCRAFT_JSON -d docs/reference/code/example/rockcraft.yaml --strict=false --spec=draft2020
+          ajv validate -s $ROCKCRAFT_JSON \
+            -d docs/reference/code/example/rockcraft.yaml \
+            --strict=false --spec=draft2020