Fix dangling old theme reference

[Etheryte]

What does this PR change?

See title, no pages should use the old theme anymore, but the login page was still looking for it.

GUI diff

Fixes login page.

• DONE

Documentation

• No documentation needed: only internal and user invisible changes

• DONE

Test coverage

ℹ️ If a major new functionality is added, it is strongly recommended that tests for the new functionality are added to the Cucumber test suite

• No tests: UI bugfix

• DONE

Links

Slack thread: https://suse.slack.com/archives/C02D134507M/p1732619812848779

• DONE

Changelogs

Make sure the changelogs entries you are adding are compliant with https://github.com/uyuni-project/uyuni/wiki/Contributing#changelogs and https://github.com/uyuni-project/uyuni/wiki/Contributing#uyuni-projectuyuni-repository

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Re-run a test

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• Re-run test "backend_unittests_pgsql"
• Re-run test "java_pgsql_tests"
• Re-run test "schema_migration_test_pgsql"
• Re-run test "susemanager_unittests"
• Re-run test "javascript_lint"
• Re-run test "spacecmd_unittests"

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[github-actions]

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Acceptance tests will take some time (aprox. 1h), please be patient ☕
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You can also check the artifacts section, which contains the logs at https://github.com/uyuni-project/uyuni/pull/9514/checks.

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Reference tests:

• https://github.com/uyuni-project/uyuni/actions/workflows/acceptance_tests_secondary_parallel.yml?query=event%3Aschedule

• https://github.com/uyuni-project/uyuni/actions/workflows/acceptance_tests_secondary.yml?query=event%3Aschedule

KNOWN ISSUES

Sometimes the build can fail when pulling new jar files from download.opensuse.org . This is a known limitation. Given this happens rarely, when it does, all you need to do is rerun the test. Sorry for the inconvenience.

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Happy hacking!
⚠️ You should not merge if acceptance tests fail to pass. ⚠️

[szachovy]

Approved for now. Will reopen if the error persists after reloading the pipelines.
EDIT: Please correct changelog to be compliant with gh actions.