Ruby: use a valid change note category

Author: asgerf

ruby/ql/lib/change-notes/2023-06-28-tracking-on-demand.md

@@ -1,5 +1,5 @@
 ---
-category: library
+category: majorAnalysis
 ---
 * The API graph library (`codeql.ruby.ApiGraphs`) has been significantly improved, with better support for inheritance,
   and data-flow nodes can now be converted to API nodes by calling `.track()` or `.backtrack()` on the node.