tests: prevent conflict markers in test case from triggering warnings

Broadly, having lines that begin with several '<' tends to trigger tools that
try to warn you about unresolved conflicts. It will save some headaches to
tweak this string literal to avoid that.

Differential Revision: https://phab.mercurial-scm.org/D3897

tests/test-simplemerge.py

@@ -109,13 +109,13 b' MERGED_RESULT = split_lines(b"""\\'
        so we may see their result.
      The two are the same,
      But after they are produced,
-       they have different names.
-<<<<<<< LAO
-=======
+       they have different names.\
+\n<<<<<<< LAO\
+\n=======
 
        -- The Way of Lao-Tzu, tr. Wing-tsit Chan
-
->>>>>>> TAO
+\
+\n>>>>>>> TAO
 """)
 
 class TestMerge3(TestCase):