extras are normalized, per PEP685

Author: dimbleby

src/poetry/core/masonry/metadata.py

@@ -6,6 +6,8 @@
 
 
 if TYPE_CHECKING:
+    from packaging.utils import NormalizedName
+
     from poetry.core.packages.package import Package
 
 
@@ -41,7 +43,7 @@ class Metadata:
 
     # Version 2.1
     description_content_type: str | None = None
-    provides_extra: list[str] = []  # noqa: RUF012
+    provides_extra: list[NormalizedName] = []  # noqa: RUF012
 
     @classmethod
     def from_package(cls, package: Package) -> Metadata: