createrepo_c: unstable test: Scenario: --update with two packages with the same NEVRA and checksums reports duplicates

[kontura]

Sometimes the test fails with the following diff:

expected                                   |  found
Directory walk started                     |  Directory walk started
Directory walk done - 2 packages           |  Directory walk done - 2 packages
Loaded information about 1 packages        |  Loaded information about 0 packages
Temporary output repo path: ./.repodata/   |  Temporary output repo path: ./.repodata/
Pool started (with 5 workers)              |  Pool started (with 5 workers)
Pool finished                              |  Pool finished
New and old repodata match, not updating.  |  New and old repodata match, not updating.