Issue #21538: The plistlib module now supports loading of binary plist files
when reference or offset size is not a power of two.
Issue #14710: Fix both pkgutil.find_loader() and get_loader() to not
raise an exception when a module doesn't exist.

Thanks to Pavel Aslanov for the bug report.
Fixed new Tkinter tests added in issue #21522 with Tk 8.4.