ESQL: Fix test (#116096)

I missed this in #116086. The test needs to have a good `toString` for
it to pass.

Closes #116094

Author: nik9000

muted-tests.yml

@@ -225,9 +225,6 @@ tests:
   issue: https://github.com/elastic/elasticsearch/issues/116050
 - class: org.elasticsearch.xpack.application.connector.ConnectorIndexServiceTests
   issue: https://github.com/elastic/elasticsearch/issues/116087
-- class: org.elasticsearch.compute.operator.FilterOperatorTests
-  method: testSimpleDescription
-  issue: https://github.com/elastic/elasticsearch/issues/116094
 - class: org.elasticsearch.xpack.searchbusinessrules.PinnedQueryBuilderIT
   method: testPinnedPromotions
   issue: https://github.com/elastic/elasticsearch/issues/116097

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/operator/FilterOperatorTests.java

@@ -53,7 +53,18 @@ public void close() {}
 
     @Override
     protected Operator.OperatorFactory simple() {
-        return new FilterOperator.FilterOperatorFactory(dvrCtx -> new SameLastDigit(dvrCtx, 0, 1));
+        return new FilterOperator.FilterOperatorFactory(new EvalOperator.ExpressionEvaluator.Factory() {
+
+            @Override
+            public EvalOperator.ExpressionEvaluator get(DriverContext context) {
+                return new SameLastDigit(context, 0, 1);
+            }
+
+            @Override
+            public String toString() {
+                return "SameLastDigit[lhs=0, rhs=1]";
+            }
+        });
     }
 
     @Override