Some artifacts can't be downloaded due to incorrect permissions

Our test suite dumps journals on test fails into $TMT_TEST_DATA directory, but since the tests run under root, the final journals have too strict permissions that prevent them from being downloaded.

For example, in this run: https://artifacts.dev.testing-farm.io/dc2d510e-95e9-4b18-81b0-6207e345255f/work-ci52qlnikq/plans/ci/execute/data/guest/default-0/integration/upstream-tests-2/ - there's a couple of journals under the data directory, but none of them can be downloaded:

$ wget https://artifacts.dev.testing-farm.io/dc2d510e-95e9-4b18-81b0-6207e345255f/work-ci52qlnikq/plans/ci/execute/data/guest/default-0/integration/upstream-tests-2/data/TEST-13-NSPAWN.journal
--2023-11-22 18:21:54--  https://artifacts.dev.testing-farm.io/dc2d510e-95e9-4b18-81b0-6207e345255f/work-ci52qlnikq/plans/ci/execute/data/guest/default-0/integration/upstream-tests-2/data/TEST-13-NSPAWN.journal
Resolving artifacts.dev.testing-farm.io (artifacts.dev.testing-farm.io)... 52.14.131.2
Connecting to artifacts.dev.testing-farm.io (artifacts.dev.testing-farm.io)|52.14.131.2|:443... connected.
HTTP request sent, awaiting response... 403 Forbidden
2023-11-22 18:21:55 ERROR 403: Forbidden.

I guess this could be resolved on our side by tweaking the permissions of stuff in $TMT_TEST_DATA, but it would be nice if TF did that automagically when exporting the artifacts to the artifact sever.