Misc: Use correct package-ecosystem in dependabot config

Use uv as the desired package-ecosystem according to the docs at
https://docs.github.com/en/code-security/reference/supply-chain-security/dependabot-options-reference#package-ecosystem-

Author: bjoernricks

.github/dependabot.yml

@@ -1,6 +1,6 @@
 version: 2
 updates:
-  - package-ecosystem: pip
+  - package-ecosystem: uv
     directory: "/"
     schedule:
       interval: weekly