chore: update milestones after 31.0.8 & 30.0.14

Signed-off-by: Benjamin Gaussorgues <benjamin.gaussorgues@nextcloud.com>

Author: Altahrim

milestoneupdater/config.json

@@ -30,19 +30,17 @@
     "viewer"
   ],
   "dueDates": {
-    "Nextcloud 30.0.13": "2025-07-10",
-    "Nextcloud 30.0.14": "2025-08-14",
-    "Nextcloud 31.0.7": "2025-07-10",
-    "Nextcloud 31.0.8": "2025-08-14"
+    "Nextcloud 30.0.15": "2025-09-11",
+    "Nextcloud 31.0.9": "2025-09-11"
   },
   "closeMilestones": [
-    "Nextcloud 31.0.7",
-    "Nextcloud 30.0.13"
+    "Nextcloud 31.0.8",
+    "Nextcloud 30.0.14"
   ],
   "addMilestones": [
-    "Nextcloud 30.0.14",
-    "Nextcloud 31.0.8"
+    "Nextcloud 30.0.15",
+    "Nextcloud 31.0.9",
+    "Nextcloud 31.0.10"
   ],
   "versionAdded": {}
 }
-