fix: keep build-system table

Signed-off-by: Frost Ming <[email protected]>

Author: frostming

src/pdm/formats/uv.py

@@ -38,7 +38,6 @@ def build_pyproject_toml(self) -> Path:
         data.setdefault("project", {})["requires-python"] = self.requires_python
         data.setdefault("project", {})["dependencies"] = []
         data.pop("dependency-groups", None)
-        data.pop("build-system", None)
         data.setdefault("project", {}).pop("optional-dependencies", None)
         sources = {}
         collected_deps: dict[str, list[str]] = {}