ESQL: Create fewer documents in lookup tests (elastic#126874)

This lowers the number of documents used to test lookup because we have
a few failures over the last few months. These are all cases that we
expect to *pass* so fewer documents should make them even more likely to
pass.

Closes elastic#125913 Closes elastic#125779

Author: nik9000

test/external-modules/esql-heap-attack/src/javaRestTest/java/org/elasticsearch/xpack/esql/heap_attack/HeapAttackIT.java

@@ -641,7 +641,7 @@ private Map<String, Object> fetchMvLongs() throws IOException {
     }
 
     public void testLookupExplosion() throws IOException {
-        int sensorDataCount = 500;
+        int sensorDataCount = 400;
         int lookupEntries = 10000;
         Map<?, ?> map = lookupExplosion(sensorDataCount, lookupEntries);
         assertMap(map, matchesMap().extraOk().entry("values", List.of(List.of(sensorDataCount * lookupEntries))));
@@ -653,7 +653,7 @@ public void testLookupExplosionManyMatches() throws IOException {
     }
 
     public void testLookupExplosionNoFetch() throws IOException {
-        int sensorDataCount = 7500;
+        int sensorDataCount = 7000;
         int lookupEntries = 10000;
         Map<?, ?> map = lookupExplosionNoFetch(sensorDataCount, lookupEntries);
         assertMap(map, matchesMap().extraOk().entry("values", List.of(List.of(sensorDataCount * lookupEntries))));