Fix charset

Author: GalLalouche

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/analysis/AnalyzerTests.java

@@ -94,6 +94,7 @@
 import org.elasticsearch.xpack.esql.session.IndexResolver;
 
 import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import java.time.Period;
 import java.util.ArrayList;
 import java.util.List;
@@ -3553,7 +3554,10 @@ private static FieldCapabilitiesIndexResponse fieldCapabilitiesIndexResponse(
         String indexName,
         Map<String, IndexFieldCapabilities> fields
     ) {
-        String indexMappingHash = new String(MessageDigests.sha256().digest(fields.toString().getBytes()));
+        String indexMappingHash = new String(
+            MessageDigests.sha256().digest(fields.toString().getBytes(StandardCharsets.UTF_8)),
+            StandardCharsets.UTF_8
+        );
         return new FieldCapabilitiesIndexResponse(indexName, indexMappingHash, fields, false, IndexMode.STANDARD);
     }