Use TypeError instead of AssertionError for no sequence

Improve/extends tests.

src/_pytest/pytester.py

@@ -1430,7 +1430,8 @@ class LineMatcher:
         :param str match_nickname: the nickname for the match function that
             will be logged to stdout when a match occurs
         """
-        assert isinstance(lines2, collections.abc.Sequence)
+        if not isinstance(lines2, collections.abc.Sequence):
+            raise TypeError("invalid type for lines2: {}".format(type(lines2).__name__))
         lines2 = self._getlines(lines2)
         lines1 = self.lines[:]
         nextline = None