fix checkstyle errors

[pkirch]

What this PR changes/adds

This PR fixes checkstyle errors in FileTransferSampleTest.java.

Why it does that

Checkstyle CI in upstream is failing.

Further notes

Downstream and upstream issues have been files to cover uncaught checkstyle errors.

Linked Issue(s)

Closes #252

Checklist

• [ ] added appropriate tests?
• [X] performed checkstyle check locally?
• [ ] added/updated copyright headers?
• [ ] documented public classes/methods?
• [ ] added/updated relevant documentation?
• [ ] added relevant details to the changelog? (skip with label no-changelog)
• [ ] formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)

[github-actions[bot]]

Unit Test Results

     416 files  ±0       416 suites  ±0   21m 14s :stopwatch: -51s 12 385 tests ±0  12 371 :heavy_check_mark: ±0  14 :zzz: ±0  0 :x: ±0  12 452 runs  ±0  12 438 :heavy_check_mark: ±0  14 :zzz: ±0  0 :x: ±0 

Results for commit c0667930. ± Comparison against base commit 7fe1bf8a.

[pkirch]

FYI, ignoring failing check Dependency Review / dependency-review (pull_request) as there are no dependencies to check in this change.

Error message:

Dependency review is not supported on this repository. Please ensure that Dependency graph is enabled, see https://github.com/agera-edc/DataSpaceConnector/settings/security_analysis