Skip irrelevant files when loading jobs from disk.

When loading from disk, skip files such as backup & temp files created
during the AtomicFile writing process to avoid incorrectly reading
duplicate jobs from them.

Bug: 289062813
Bug: 305169670
Test: atest FrameworksServicesTests:JobStoreTest
Change-Id: I28a180e2b24357219d34be6a22c785311be6e72e