fix: Fix handling of "format" in package includes initialization

Ensure that "format" is always processed as a list when initializing package includes. If not explicit set default to sdist and wheel.

src/poetry/core/masonry/utils/module.py

@@ -72,11 +72,15 @@ def __init__(
             packages = [default_package]
 
         for package in packages:
+            formats = package.get("format", ["sdist", "wheel"])
+            if formats and not isinstance(formats, list):
+                formats = [formats]
+
             self._package_includes.append(
                 PackageInclude(
                     self._path,
                     package["include"],
-                    formats=package["format"],
+                    formats=formats,
                     source=package.get("from"),
                     target=package.get("to"),
                 )