declare artifact_content variable to avoid reference before assignmen…

[sa3eed3ed]

…t in case of exception

in case the content is not UTF-8 encoded an exception will be raised and artifact_content will never be assigned, this cause the task to fail with a misleading exception: [local variable 'artifact_content' referenced before assignment], while it should be Artifact {evidence.artifact_name} has empty content or not UTF-8 encoded

Description of the change

Applicable issues

• fixes #

Additional information

Checklist

• [ ] All tests were successful.
• [ ] Unit tests added.
• [ ] Documentation updated.