Add test and fix changelog for schema_cache_ignored_table?

Author: eileencodes

activerecord/CHANGELOG.md

@@ -4,7 +4,7 @@
 
     ```ruby
     ActiveRecord.schema_cache_ignored_tables = ["developers"]
-    ActiveRecord.schema_cache_ignored_tables?("developers")
+    ActiveRecord.schema_cache_ignored_table?("developers")
     => true
     ```
 

activerecord/test/cases/connection_adapters/schema_cache_test.rb

@@ -231,7 +231,9 @@ def test_marshal_dump_and_load_via_disk
 
       def test_marshal_dump_and_load_with_ignored_tables
         old_ignore = ActiveRecord.schema_cache_ignored_tables
+        assert_not ActiveRecord.schema_cache_ignored_table?("professors")
         ActiveRecord.schema_cache_ignored_tables = ["professors"]
+        assert ActiveRecord.schema_cache_ignored_table?("professors")
         # Create an empty cache.
         cache = new_bound_reflection