Update packse and remove Python 3.9.20 from test requirements (#17881)

Requires the packse PR to land first.

scripts/sync-python-version-constants.py

@@ -2,7 +2,7 @@
 
 This script reads the download-metadata.json file and extracts the latest
 patch version for each minor version (3.15, 3.14, 3.13, 3.12, 3.11, 3.10).
-It then updates the LATEST_PYTHON_X_Y constants in crates/uv/tests/it/common/mod.rs.
+It then updates the LATEST_PYTHON_X_Y constants in crates/uv-test/src/lib.rs.
 
 For minor versions with stable releases, it uses the latest stable version.
 For minor versions with only prereleases, it uses the latest prerelease.
@@ -70,7 +70,7 @@ def main() -> None:
         if minor not in latest_versions:
             latest_versions[minor] = prerelease_versions[minor]
 
-    # Update the constants in common/mod.rs
+    # Update the constants in uv-test/src/lib.rs
     lib_path = ROOT / "crates" / "uv-test" / "src" / "lib.rs"
     content = lib_path.read_text()