py3: fix test-propertycache.py

Differential Revision: https://phab.mercurial-scm.org/D5101

tests/test-propertycache.py

@@ -11,6 +11,7 b' import subprocess'
 from mercurial import (
     hg,
     localrepo,
+    pycompat,
     ui as uimod,
     util,
 )
@@ -44,7 +45,7 b' localrepo.localrepository.testcachedunfi'
 
 # Create an empty repo and instantiate it. It is important to run
 # these tests on the real object to detect regression.
-repopath = os.path.join(os.environ['TESTTMP'], 'repo')
+repopath = pycompat.fsencode(os.path.join(os.environ['TESTTMP'], 'repo'))
 assert subprocess.call(['hg', 'init', repopath]) == 0
 ui = uimod.ui.load()
 repo = hg.repository(ui, path=repopath).unfiltered()