fix GeoHashGridTests precision parsing error

Previously, a hardcoded precision value of 4 was
used by these tests resulting in no approximation
errors. Now that the precision is between 1-12,
precision values of 1 and 2 result in potential
bucketing errors.

This commit adjusts the range to be 4-12.

Fixes #37892.

server/src/test/java/org/elasticsearch/search/aggregations/bucket/geogrid/GeoHashGridTests.java

@@ -51,6 +51,6 @@ public class GeoHashGridTests extends GeoGridTestCase<InternalGeoHashGridBucket,
 
     @Override
     protected int randomPrecision() {
-        return randomIntBetween(1, 12);
+        return randomIntBetween(4, 12);
     }
 }