assertions.rb: return the exception

* test/lib/test/unit/assertions.rb (assert_syntax_error): return
  the rescued exception object as well as assert_raise.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54653 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/lib/test/unit/assertions.rb

@@ -495,6 +495,7 @@ EOT
           catch {|tag| eval(code, binding, fname, line)}
         end
         assert_match(error, e.message, mesg)
+        e
       ensure
         $VERBOSE = verbose
       end