Fix synchronization in external source tests

[jantonguirao]

Signed-off-by: Joaquin Anton [email protected]

Category:

Other (bugfix in test code)

Description:

It fixes synchronization in external source tests. Fixes https://github.com/NVIDIA/DALI/issues/4151

Additional information:

Affected modules and functionalities:

External source tests

Key points relevant for the review:

NA

Tests:

• [x] Existing tests apply
• [ ] New tests added
  • [ ] Python tests
  • [ ] GTests
  • [ ] Benchmark
  • [ ] Other
• [ ] N/A

Checklist

Documentation

• [ ] Existing documentation applies
• [ ] Documentation updated
  • [ ] Docstring
  • [ ] Doxygen
  • [ ] RST
  • [ ] Jupyter
  • [ ] Other
• [x] N/A

DALI team only

Requirements

• [ ] Implements new requirements
• [ ] Affects existing requirements
• [x] N/A

REQ IDs: N/A

JIRA TASK: N/A