Fix first release date of Python 3.14

See https://peps.python.org/pep-0745/

Author: m-aciek

include/release-cycle.json

@@ -11,7 +11,7 @@
     "branch": "3.14",
     "pep": 745,
     "status": "prerelease",
-    "first_release": "2025-10-01",
+    "first_release": "2025-10-07",
     "end_of_life": "2030-10",
     "release_manager": "Hugo van Kemenade"
   },