Fix test for libsystemd v250

[daipom]

This will fix the failing test in following RP.

• 100

The latest libsystemd can read some corrupted entries without errors.

Since libsystemd v250, it's specification against journal file corruption changed.

https://github.com/systemd/systemd/blob/v250/NEWS#L807-L808

• https://github.com/systemd/systemd/commit/df207ccb7be02b1ca6bdd0a2066a898e5b24ee86
• https://github.com/systemd/systemd/commit/548614cc9a1d7cb4ad84923b42a6e18591eaf5dd

In AlmaLinux9 (libsystemd v250):

require "systemd"
require "systemd/journal"
journal = Systemd::Journal.new(path: "test/fixture/corrupt")
entries = journal.to_a # Succeeds without errors
entries[2] # Before v250, it couldn't read this entry.
=> #<Systemd::JournalEntry:0x000000000003ba60 priority: '6',
_boot_id: '4737ffc504774b3ba67020bc947f1bc0', _machine_id:
'bb9d0a52a41243829ecd729b40ac0bce', _hostname: 'arch',
_source_monotonic_timestamp: '0', _transport: 'kernel',
syslog_identifier: 'kernel'>

Assuming both old and new libsystemd, it would be good to fix the test in this way.