[suggest] Use realpath to canonicalize path in test (#7526)

The tmp_dir we computed and the real path that was showing up in
the output didn't match on OS X in the testSuggestColonMethodJSON
test. Use realpath to fix the issue.

Author: msullivan

mypy/test/testfinegrained.py

@@ -290,7 +290,7 @@ def maybe_suggest(self, step: int, server: Server, src: str, tmp_dir: str) -> Li
             if json:
                 # JSON contains already escaped \ on Windows, so requires a bit of care.
                 val = val.replace('\\\\', '\\')
-                val = val.replace(tmp_dir + os.path.sep, '')
+                val = val.replace(os.path.realpath(tmp_dir) + os.path.sep, '')
             output.extend(val.strip().split('\n'))
         return normalize_messages(output)