bpo-37124: Fix reference leak in test_msilib (GH-13750) (GH-14340)

(cherry picked from commit c0295db)

Author: vstinner

Lib/test/test_msilib.py

@@ -45,6 +45,7 @@ def test_summaryinfo_getproperty_issue1104(self):
 
     def test_directory_start_component_keyfile(self):
         db, db_path = init_database()
+        self.addCleanup(msilib._directories.clear)
         feature = msilib.Feature(db, 0, 'Feature', 'A feature', 'Python')
         cab = msilib.CAB('CAB')
         dir = msilib.Directory(db, cab, None, TESTFN, 'TARGETDIR',