Removal of empty username support in keyring 25.3.0 breaks several tests

[musicinmybrain]

$ gh repo clone jaraco/keyrings.alt
$ cd keyrings.alt
$ tox
[…]
=========================================================================================== short test summary info ============================================================================================
FAILED tests/mocks.py::ruff
FAILED tests/test_crypto.py::TestCryptedFileKeyring::test_empty_username - ValueError: Username cannot be blank.
FAILED tests/test_file.py::TestEncryptedFileKeyring::test_empty_username[Crypto] - ValueError: Username cannot be blank.
FAILED tests/test_file.py::TestEncryptedFileKeyring::test_empty_username[Cryptodome] - ValueError: Username cannot be blank.
FAILED tests/test_file.py::TestUncryptedFileKeyring::test_empty_username - ValueError: Username cannot be blank.
================================================================================== 5 failed, 154 passed, 81 skipped in 9.05s ===================================================================================

[musicinmybrain]

While this appears to be triggered by jaraco/keyring#687, the ValueError comes from keyrings.alt:

keyrings.alt/keyrings/alt/file_base.py

Line 118 in c821934

raise ValueError("Username cannot be blank.")

[mitya57]

I submitted PR #55 which is one of possible solutions for this.