Dependabot: only update npm lockfile (#2277)

.github/dependabot.yml

@@ -33,3 +33,4 @@ updates:
     directory: "/requirements"
     schedule:
       interval: "weekly"
+    versioning-strategy: "lockfile-only"

requirements/package.json

@@ -2,6 +2,6 @@
   "name": "torchgeo",
   "private": "true",
   "dependencies": {
-    "prettier": ">=3.3.3"
+    "prettier": ">=3"
   }
 }