Fix my test introduced in test_sys by r79394:

Victor Stinner · Victor Stinner · commit 4ce881e928fc · 2010-03-25T12:24:38.000Z
Restore the orginal filesystem encoding before testing
assertRaises(LookupError, sys.setfilesystemencoding, "xxx"). Unittest formats
the exception, but the formatting failed because the file system was invalid
(set to iso-8859-1 by the previous test).

Anyway, ensure to restore the original filesystem encoding when exiting
test_setfilesystemencoding() to avoid error propagation to the other tests.
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
@@ -797,10 +797,15 @@ def test_pythontypes(self):
 
     def test_setfilesystemencoding(self):
         old = sys.getfilesystemencoding()
-        sys.setfilesystemencoding("iso-8859-1")
-        self.assertEqual(sys.getfilesystemencoding(), "iso-8859-1")
-        self.assertRaises(LookupError, sys.setfilesystemencoding, "xxx")
-        sys.setfilesystemencoding(old)
+        try:
+            sys.setfilesystemencoding("iso-8859-1")
+            self.assertEqual(sys.getfilesystemencoding(), "iso-8859-1")
+        finally:
+            sys.setfilesystemencoding(old)
+        try:
+            self.assertRaises(LookupError, sys.setfilesystemencoding, "xxx")
+        finally:
+            sys.setfilesystemencoding(old)
 
 def test_main():
     test.support.run_unittest(SysModuleTest, SizeofTest)
