Pickle closed-file loading test exercises dumping instead of loading #159361

In Lib/test/pickletester.py, test_load_closed_file calls self.dump, duplicating test_dump_closed_file instead of exercising self.load on a closed file.

The existing assertion is:

self.assertRaises(ValueError, self.dump, 123, f)

The loading test should open a readable binary file, close it, and assert that self.load(f) raises ValueError. This restores coverage of the intended failure path for both Python and C pickle implementations.

Verified on CPython main at 9ed41860b411144dbb6d2e4f53489d432364fd19: the corrected cases pass with the real loaders and fail when the loaders are replaced with no-ops. The complete test_pickle module passed on a Windows debug build.

Linked PRs

• gh-159361: Exercise load in the pickle closed-file test #159332