Change test locale


### Discussed in https://github.com/redhat-developer/vscode-extension-tester/discussions/1540

<div type='discussions-op-text'>

<sup>Originally posted by **daniel-a126** September 24, 2024</sup>
Is it possible to force locale for an extest run - the same as I'd do with `--locale <locale>` command line parameter?

Thank you!</div>