run-tests: skipped test should not produce 'i' mark while retesting

When '--retest' option is enabled then skipped test should not produce 'i' mark.
This fixes a regression introduced by 92a6b16c9186 and about 200 previous
changesets from Gregory Szorc.

tests/run-tests.py

@@ -1106,6 +1106,7 b' class TestResult(unittest._TextTestResul'
         if self.showAll:
             self.stream.writeln('ignored %s' % reason)
         else:
+            if reason != 'not retesting':
             self.stream.write('i')
             self.stream.flush()