non-latin chars to tests fail on Launchpad

### Bug Description

A regression since https://github.com/mixxxdj/mixxx/pull/15722

This unfortunately fails at Launchpad. Interestingly not with every distro. 
https://launchpad.net/~mixxx/+archive/ubuntu/mixxxbetas/+build/32978804
https://launchpad.net/~mixxx/+archive/ubuntu/nightlies/+build/32979033
https://launchpad.net/~mixxx/+archive/ubuntu/nightlies/+build/32978843

 ```
 Note: Google Test filter = TrackExporterTest.SimpleListExport
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from TrackExporterTest
[ RUN      ] TrackExporterTest.SimpleListExport
warning [0x5ab08a6417f0] TrackExportWorker - File not found or inaccessible while exporting QFileInfo(/<<PKGBUILDDIR>>/src/test/id3-test-data/cover-test-øé~ł€˚.ogg)
warning [0x5ab08a6417f0] TrackExportWorker - File not found or inaccessible while exporting QFileInfo(/<<PKGBUILDDIR>>/src/test/id3-test-data/cover-test-øé~ł€˚.flac)
warning [0x5ab08a6417f0] TrackExportWorker - File not found or inaccessible while exporting QFileInfo(/<<PKGBUILDDIR>>/src/test/id3-test-data/cover-test-øé~ł€˚-ffmpeg-aac.m4a)
./src/test/trackexport_test.cpp:67: Failure
Expected equality of these values:
  3
  m_answerer->currentProgress()
    Which is: 0

./src/test/trackexport_test.cpp:68: Failure
Expected equality of these values:
  3
  m_answerer->currentProgressCount()
    Which is: 0

./src/test/trackexport_test.cpp:71: Failure
Value of: QFileInfo::exists(m_exportDir.filePath(kOggTestFile))
  Actual: false
Expected: true

./src/test/trackexport_test.cpp:72: Failure
Value of: QFileInfo::exists(m_exportDir.filePath(kFlacTestFile))
  Actual: false
Expected: true

./src/test/trackexport_test.cpp:73: Failure
Value of: QFileInfo::exists(m_exportDir.filePath(kM4aAacTestFile))
  Actual: false
Expected: true

[  FAILED  ] TrackExporterTest.SimpleListExport (1 ms)
[----------] 1 test from TrackExporterTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] TrackExporterTest.SimpleListExport

 1 FAILED TEST
 ```

I will file an issue. 

### Version

2.6-beta

### OS

Ubuntu

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