Maintenance: Update dependency graphql to v2.3.15

Gemfile.lock

@@ -263,7 +263,7 @@ GEM
     gli (2.21.1)
     globalid (1.2.1)
       activesupport (>= 6.1)
-    graphql (2.3.14)
+    graphql (2.3.15)
       base64
       fiber-storage
     graphql-batch (0.6.0)