pythongh-134455: Fix build-details.json to use the c_api.headers key (python#134456)

Fix `build-details.json` generation to use the correct `c_api.headers`
key as defined in PEP 739, instead of `c_api.include`.

Co-authored-by: Filipe Laíns 🇵🇸 <[email protected]>

Author: mgorny

Misc/NEWS.d/next/Build/2025-05-21-19-46-28.gh-issue-134455.vdwlrq.rst

@@ -0,0 +1,2 @@
+Fixed ``build-details.json`` generation to use the correct ``c_api.headers``
+as defined in :pep:`739`, instead of ``c_api.include``.

Tools/build/generate-build-details.py

@@ -123,7 +123,7 @@ def generate_data(schema_version: str) -> collections.defaultdict[str, Any]:
     if has_static_library:
         data['libpython']['static'] = os.path.join(LIBDIR, LIBRARY)
 
-    data['c_api']['include'] = INCLUDEDIR
+    data['c_api']['headers'] = INCLUDEDIR
     if LIBPC:
         data['c_api']['pkgconfig_path'] = LIBPC