Ensure collation is set to database default when changing column

A recent change made it so that when you perform a change column
it will preserve collation on the column rather than nil it out·
which would select the database default. This works fine except in
the case of a binary type. In this case the collation should be
set to nil in the options so that the database default collation
type can be used on the column.

Author: ahoglund

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -398,7 +398,7 @@ def build_change_column_definition(table_name, column_name, type, **options) # :
           options[:comment] = column.comment
         end
 
-        unless options.key?(:collation)
+        unless options.key?(:collation) || type == :binary
           options[:collation] = column.collation
         end
 

activerecord/test/cases/adapters/mysql2/charset_collation_test.rb

@@ -48,6 +48,16 @@ class Mysql2CharsetCollationTest < ActiveRecord::Mysql2TestCase
     assert_equal "utf8mb4_general_ci", column.collation
   end
 
+  test "change column ensures binary column type are set to nil" do
+    @connection.add_column :charset_collations, :description, :string, charset: "utf8mb4", collation: "utf8mb4_unicode_ci"
+    @connection.change_column :charset_collations, :description, :binary
+
+    column = @connection.columns(:charset_collations).find { |c| c.name == "description" }
+
+    assert_equal :binary, column.type
+    assert_nil column.collation
+  end
+
   test "change column preserves collation" do
     @connection.add_column :charset_collations, :description, :string, charset: "utf8mb4", collation: "utf8mb4_unicode_ci"
     @connection.change_column :charset_collations, :description, :text