test/system: Limit the scope of temporary files used by all tests

[debarshiray]

BATS_RUN_DIR is the directory used by Bats for its own internal temporary files, and BATS_SUITE_TMPDIR is for creating files common to all tests in the test suite [1]. It's better to stay away from Bats' own internal temporary files to avoid unexpected collisions.

[1] https://bats-core.readthedocs.io/en/stable/writing-tests.html

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/local/buildset/39ea880b8e0a4e30a88c56bc351a0d9b

:heavy_check_mark: unit-test SUCCESS in 4m 46s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 6m 06s :heavy_check_mark: unit-test-restricted SUCCESS in 4m 51s :heavy_check_mark: system-test-fedora-rawhide SUCCESS in 36m 03s :heavy_check_mark: system-test-fedora-39 SUCCESS in 36m 38s :heavy_check_mark: system-test-fedora-38 SUCCESS in 33m 39s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/local/buildset/ed68f8baaa124fb2b164233d86595fb2

:heavy_check_mark: unit-test SUCCESS in 4m 46s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 3m 25s :heavy_check_mark: unit-test-restricted SUCCESS in 3m 52s :heavy_check_mark: system-test-fedora-rawhide SUCCESS in 37m 26s :heavy_check_mark: system-test-fedora-39 SUCCESS in 31m 38s :heavy_check_mark: system-test-fedora-38 SUCCESS in 39m 19s