test_sprintf_comb.rb: split tests

* test/ruby/test_sprintf_comb.rb (test_format_integer),
  (test_format_float): split huge tests by the formats.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42908 b2dd03c8-39d4-4d8f-98ff-823fe69b080e