run-tests: fix a typo in an attribute name

At least, I assume it's a typo.  Nothing else uses it, but `_tmpbindir` is used.

Differential Revision: https://phab.mercurial-scm.org/D9542

tests/run-tests.py

@@ -2948,7 +2948,7 b' class TestRunner(object):'
         self._hgtmp = None
         self._installdir = None
         self._bindir = None
-        self._tmpbinddir = None
+        self._tmpbindir = None
         self._pythondir = None
         self._coveragefile = None
         self._createdfiles = []