Stabilize more flaky tests

[laserprec]

Description

We have some flaky smoke & integration tests that are failing our nightly run every now and then. Adding flaky markers so these tests can be reran without failing the build.

Example failures: https://github.com/microsoft/recommenders/actions/runs/1384618134

Nightly build status with the current changes:

Checklist:

• I have followed the contribution guidelines and code style for this project.
• I have added tests covering my contributions.
• I have updated the documentation accordingly.
• This PR is being made to staging branch and not to main branch.

[miguelgfierro]

@laserprec this is really nice, we had other super flaky tests https://github.com/microsoft/recommenders/blob/main/tests/unit/recommenders/datasets/test_wikidata.py that were skipped. Can we try this marker there and check if it works?