Use max rather than min to sort managed Pythons (#5205)

## Summary

See: https://github.com/astral-sh/uv/issues/5139 and
https://github.com/astral-sh/uv/pull/5201#discussion_r1683636935.

## Test Plan

Verified that 3.12 was chosen above 3.8 in:

- `cargo run -- python uninstall --all`
- `cargo run -- python install 3.8 3.12`
- `cargo run -- tool run -v httpx`

crates/uv-python/src/implementation.rs

@@ -12,16 +12,16 @@ pub enum Error {
 
 #[derive(Debug, Eq, PartialEq, Clone, Copy, Default, PartialOrd, Ord, Hash)]
 pub enum ImplementationName {
+    GraalPy,
+    PyPy,
     #[default]
     CPython,
-    PyPy,
-    GraalPy,
 }
 
 #[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash)]
 pub enum LenientImplementationName {
-    Known(ImplementationName),
     Unknown(String),
+    Known(ImplementationName),
 }
 
 impl ImplementationName {