Uncomment some tests (dart-lang/yaml#145)

These tests had been commented out since the original commit in this
repo even though most of them would pass.

With these tests commented out the suite has an empty `group` which may
become disallowed.
https://github.com/dart-lang/test/issues/1961

Change double quotes to single quotes.

Skip a test which is currently failing due to an error parsing a float
value with a single digit.