fix(ci): correct transformer backend path typo (#8712)

* fix(ci): correct transformer backend path typo

- Fix typo: 'transformer' -> 'transformers' in .github/workflows/test.yml
- The original PR #8710 had a typo where 'transformers' was written as 'transformer'
- This caused the build to fail as the directory is actually named 'transformers'
- References: https://github.com/mudler/LocalAI/pull/8710

* Apply suggestion from @mudler

Signed-off-by: Ettore Di Giacinto <mudler@users.noreply.github.com>

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Signed-off-by: Ettore Di Giacinto <mudler@users.noreply.github.com>
Co-authored-by: localai-bot <localai-bot@users.noreply.github.com>
Co-authored-by: Ettore Di Giacinto <mudler@users.noreply.github.com>