Always close files in distutils code and tests (#10252).

Lib/distutils/command/bdist_wininst.py

@@ -340,4 +340,8 @@ class bdist_wininst(Command):
             sfix = ''
 
         filename = os.path.join(directory, "wininst-%.1f%s.exe" % (bv, sfix))
-        return open(filename, "rb").read()
+        f = open(filename, "rb")
+        try:
+            return f.read()
+        finally:
+            f.close()