Fix test 13

[cferreiragonz]

Description

This PR fixes test 13 of discovery server by correctly setting the timestamp of snapshot test_13_disposals_single_server_a.P1_-_b.S1. For some reason, this snapshot was not reflecting the test chronology described at the beginning of the test case. This was corrected during the Discovery Server refactor in master, but it was never backported. The test started failing after eProsima/Fast-DDS#5556.

Contributor Checklist

• Commit messages follow the project guidelines.
• The added tests pass locally.
• N/A Changes are backwards compatible.
• N/A New feature has been documented/Current behavior is correctly described in the documentation.
• N/A Applicable backports have been included in the description.

Reviewer Checklist

• The PR has a milestone assigned.
• The title and description correctly express the PR's purpose.
• Check contributor checklist is correct.
• Check CI results: changes do not issue any warning.
• Check CI results: failing tests are unrelated with the changes.

[MiguelCompany]

LGTM