Reduce the max depth of randomly generated interval queries (#50317)

We randomly generate intervals sources to test serialization and query generation
in IntervalQueryBuilderTests. However, rarely we can generate a query that has
too many nested disjunctions, resulting in query rewrites running afoul of the maximum
boolean clause limit.

This commit reduces the maximum depth of the randomly generated intervals source
to make running into this limit much more unlikely.

server/src/test/java/org/elasticsearch/index/query/IntervalQueryBuilderTests.java

@@ -86,7 +86,7 @@ protected void initializeAdditionalMappings(MapperService mapperService) throws
     }
 
     private IntervalsSourceProvider createRandomSource(int depth, boolean useScripts) {
-        if (depth > 3) {
+        if (depth > 2) {
             return createRandomMatch(depth + 1, useScripts);
         }
         switch (randomInt(20)) {