fix: stored source mode not supported in 8.16

We also update a few error messages to account
for a few minor differences.

Author: salvatore-campagna

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/dataframe/DataFrameAnalyticsSource.java

@@ -96,7 +96,7 @@ public DataFrameAnalyticsSource(
         }
         this.queryProvider = queryProvider == null ? QueryProvider.defaultQuery() : queryProvider;
         if (sourceFiltering != null && sourceFiltering.fetchSource() == false) {
-            throw new IllegalArgumentException("source._source cannot be disabled");
+            throw new IllegalArgumentException("source._source can not be disabled");
         }
         this.sourceFiltering = sourceFiltering;
         this.runtimeMappings = runtimeMappings == null ? Collections.emptyMap() : Collections.unmodifiableMap(runtimeMappings);

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/ml/dataframe/DataFrameAnalyticsSourceTests.java

@@ -104,7 +104,7 @@ public void testConstructor_GivenDisabledSource() {
             IllegalArgumentException.class,
             () -> new DataFrameAnalyticsSource(new String[] { "index" }, null, FetchSourceContext.DO_NOT_FETCH_SOURCE, null)
         );
-        assertThat(e.getMessage(), equalTo("source._source cannot be disabled"));
+        assertThat(e.getMessage(), equalTo("source._source can not be disabled"));
     }
 
     public void testConstructor_GivenInvalidRuntimeMappings() {