Add support for --system-site-packages in uv venv (#2101)

## Summary

Adds support for `--system-site-packages`. Unlike `pip`, we won't take
the system site packages into account in subsequent commands. I think
this is ok.

Closes https://github.com/astral-sh/uv/issues/1483.

crates/uv-build/src/lib.rs

@@ -402,6 +402,7 @@ impl SourceBuild {
             &temp_dir.path().join(".venv"),
             interpreter.clone(),
             gourgeist::Prompt::None,
+            false,
             Vec::new(),
         )?;