tests: use native string type for parsed hghave log lines

Before this change, on Python 2, the parsed messages were decoded to unicode,
causing an implicit conversion from unicode to str later.

tests/run-tests.py

@@ -2067,12 +2067,10 b' class TTest(Test):'
         for line in lines:
             if line.startswith(TTest.SKIPPED_PREFIX):
                 line = line.splitlines()[0]
-                missing.append(
-                    line[len(TTest.SKIPPED_PREFIX) :].decode('utf-8')
-                )
+                missing.append(_bytes2sys(line[len(TTest.SKIPPED_PREFIX) :]))
             elif line.startswith(TTest.FAILED_PREFIX):
                 line = line.splitlines()[0]
-                failed.append(line[len(TTest.FAILED_PREFIX) :].decode('utf-8'))
+                failed.append(_bytes2sys(line[len(TTest.FAILED_PREFIX) :]))
 
         return missing, failed