Bump transformers from 4.19.2 to 4.38.0 in /requirements

Bumps [transformers](https://github.com/huggingface/transformers) from 4.19.2 to 4.38.0.
- [Release notes](https://github.com/huggingface/transformers/releases)
- [Commits](huggingface/transformers@v4.19.2...v4.38.0)

---
updated-dependencies:
- dependency-name: transformers
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

requirements/optional.txt

@@ -19,4 +19,4 @@ test-tube>=0.7.5
 timm
 torch-fidelity==0.3.0
 torchmetrics==0.6.0
-transformers==4.19.2
+transformers==4.38.0