[Tests] Fix failure due to changes exception message (elastic#32036)

Java 11 seems to get more verbose on the ClassCastException we check for in
SearchDocumentationIT. This changes the test from asserting the exact exception
message to only checking the two classes involved are part of the message.

Closes elastic#32029

client/rest-high-level/src/test/java/org/elasticsearch/client/documentation/SearchDocumentationIT.java

@@ -337,8 +337,9 @@ public void testSearchRequestAggregations() throws IOException {
                     Range range = aggregations.get("by_company"); // <1>
                     // end::search-request-aggregations-get-wrongCast
                 } catch (ClassCastException ex) {
-                    assertEquals("org.elasticsearch.search.aggregations.bucket.terms.ParsedStringTerms"
-                            + " cannot be cast to org.elasticsearch.search.aggregations.bucket.range.Range", ex.getMessage());
+                    String message = ex.getMessage();
+                    assertThat(message, containsString("org.elasticsearch.search.aggregations.bucket.terms.ParsedStringTerms"));
+                    assertThat(message, containsString("org.elasticsearch.search.aggregations.bucket.range.Range"));
                 }
                 assertEquals(3, elasticBucket.getDocCount());
                 assertEquals(30, avg, 0.0);