exclude encryption performance from builds

Rails is not running encryption performance test on builds.

Commit rails/rails@1fff866) claims they were meant to be excluded from builds.
The commit also includes the same flaky test failure we have now.

Update `ar_cases` to exclude encryption performance tests

Author: mgrunberg

test/support/rake_helpers.rb

@@ -25,7 +25,9 @@ def sqlserver_cases
 
 def ar_cases
   @ar_cases ||= begin
-    Dir.glob("#{ARTest::SQLServer.root_activerecord}/test/cases/**/*_test.rb").reject { |x| x =~ /\/adapters\// }.sort
+    Dir.glob("#{ARTest::SQLServer.root_activerecord}/test/cases/**/*_test.rb").reject {
+      |x| x.include?("/adapters/") || x.include?("/encryption/performance")
+    }.sort
   end
 end