profiling: disable the import-error warning for the flamegraph module

The module being missing is properly handled, but pytype was complaining.

Differential Revision: https://phab.mercurial-scm.org/D7469

mercurial/profiling.py

@@ -77,7 +77,7 b' def lsprofile(ui, fp):'
 @contextlib.contextmanager
 def flameprofile(ui, fp):
     try:
-        from flamegraph import flamegraph
+        from flamegraph import flamegraph  # pytype: disable=import-error
     except ImportError:
         raise error.Abort(
             _(