Install Python versions with previous uv release (#5717)

Part of #5713

Shaves 50s or ~25% off the Ubuntu test run. Maybe 30s or 8% off macOS.
Windows already uses the GitHub distributions.

Note this is some of our only test coverage for Python version installs,
we may want to add separate coverage to compensate.

.github/workflows/ci.yml

@@ -156,7 +156,8 @@ jobs:
 
       - name: "Install required Python versions"
         run: |
-          cargo run python install
+          curl -LsSf https://astral.sh/uv/install.sh | sh
+          uv python install
 
       - name: "Install cargo nextest"
         uses: taiki-e/install-action@v2
@@ -193,7 +194,8 @@ jobs:
 
       - name: "Install required Python versions"
         run: |
-          cargo run python install
+          curl -LsSf https://astral.sh/uv/install.sh | sh
+          uv python install
 
       - name: "Install cargo nextest"
         uses: taiki-e/install-action@v2