Improve flaky e2e tests

[Kr0nox]

Previously the generated options for the distribution diagram test looked like this:

[
  [ 'Average Similarity', 'Linear' ],
  [ 'Maximum Similarity', 'Linear' ],
  [ 'Average Similarity', 'Linear' ],
  [ 'Average Similarity', 'Logarithmic' ]
]

Now, they do not include a duplicate case:

[
  [ 'Average Similarity', 'Linear' ],
  [ 'Maximum Similarity', 'Linear' ],
  [ 'Average Similarity', 'Logarithmic' ]
]

[sonarcloud]

Quality Gate passed for 'JPlag Report Viewer'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud