[jakduch]

What

Declare observer in the test-only dependency group, with automatic requiring disabled like the existing factory_bot_rails declaration.

Why

Foreman's current factory_bot 5.x test dependency requires observer. Ruby 3.4 moved that library out of its default gems, so the test suite cannot load on newer Ruby even when the application itself boots successfully.

This keeps the existing factory API and production dependency set unchanged. A major factory_bot upgrade is a separate change, not required to fix this missing test dependency.

Reproduction: https://github.com/jakduch/foreman/actions/runs/38786115767/job/116598424745

Testing

• Ruby 4.0.7 / Ubuntu 26.04 verification now gets past the reproduced observer LoadError: Rubocop, boot, migrations, schema restoration, the targeted Foreman logging tests and standalone factory_bot loading all passed. The full Ruby 4 unit suite is running next; full application compatibility is not claimed by this dependency-only fix.
• The same integration workflow passed on Ruby 3.0 / Ubuntu 24.04 and Ruby 3.3 / Ubuntu 26.04: Rubocop, boot, schema round trip, standalone factory loading and the logging suite (12 tests, 22 assertions, no failures/errors/skips on each). It includes the independent syslog (Fixes #39912 - Declare the syslog logging dependency #11337), PostgreSQL CI (Fixes #39911 - Match PostgreSQL dump clients in CI #11336), ldap_fluff and safemode prerequisites to reach this test stage. None of those changes or temporary Git overrides are included in this one-line PR.

Tested revision: abfbc57d3b6f1f9ffe71e6774d93d41fc13f141d.

Issue: https://projects.theforeman.org/issues/39913
Related tracking: https://projects.theforeman.org/issues/39910

AI assistance: Codex.

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