test_basicinstructions.rb: fix typo

* test/ruby/test_basicinstructions.rb (test_send_opassign): fix typo.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39123 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
test_basicinstructions.rb: implementation defined

* test/ruby/test_basicinstructions.rb (test_send_opassign):
  implementation defined behavior.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39124 b2dd03c8-39d4-4d8f-98ff-823fe69b080e