AbstractSniffUnitTest: bug fix - warnings not counted in total
AbstractSniffUnitTest: bug fix - warnings not counted in total

At the bottom of a test run a message along the lines of `4 sniff test files generated 2 unique error codes; 0 were fixable (0%)` is shown.

The unique error codes, as well as the fixable count and percentage would only include `error` codes and would totally disregard the codes coming from `warning`s.

Fixed now.

squizlabs/PHP_CodeSniffer,squizlabs/PHP_CodeSniffer,stronk7/PHP_CodeSniffer,jrfnl/PHP_CodeSniffer,jrfnl/PHP_CodeSniffer,stronk7/PHP_CodeSniffer,squizlabs/PHP_CodeSniffer,jrfnl/PHP_CodeSniffer,stronk7/PHP_CodeSniffer