.github/workflows: Enable more tests on Ubuntu 22.04 by setting SHELL

[debarshiray]

The SHELL environment variable goes mysteriously missing from the runtime environment of the GitHub Actions workflow [1]. This breaks the create and enter commands with:

  Error: failed to get the current user's default shell

... and therefore tests involving them can't be run until this is resolved.

It's been a year since this problem was first encountered and no solution is in sight. Therefore, it will be better to work around this by explicitly setting the SHELL environment variable on Ubuntu 22.04 to increase the number of tests run by the CI.

[1] https://github.com/orgs/community/discussions/59413

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/local/buildset/f5f7f1709b1e41169d2b767ae6dc4632

:heavy_check_mark: unit-test SUCCESS in 7m 06s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 4m 24s :heavy_check_mark: unit-test-restricted SUCCESS in 5m 40s :heavy_check_mark: system-test-fedora-rawhide SUCCESS in 39m 36s :heavy_check_mark: system-test-fedora-40 SUCCESS in 37m 56s :heavy_check_mark: system-test-fedora-39 SUCCESS in 38m 31s :heavy_check_mark: system-test-fedora-38 SUCCESS in 38m 05s

[softwarefactory-project-zuul[bot]]

Build succeeded. https://softwarefactory-project.io/zuul/t/local/buildset/55957991b5f84faeb2fef520b9905cf2

:heavy_check_mark: unit-test SUCCESS in 6m 26s :heavy_check_mark: unit-test-migration-path-for-coreos-toolbox SUCCESS in 3m 42s :heavy_check_mark: unit-test-restricted SUCCESS in 5m 32s :heavy_check_mark: system-test-fedora-rawhide SUCCESS in 38m 41s :heavy_check_mark: system-test-fedora-40 SUCCESS in 37m 05s :heavy_check_mark: system-test-fedora-39 SUCCESS in 36m 30s :heavy_check_mark: system-test-fedora-38 SUCCESS in 36m 29s