Bump optimum[openvino] from 1.20.0 to 1.21.2 in /samples

Bumps [optimum[openvino]](https://github.com/huggingface/optimum) from 1.20.0 to 1.21.2.
- [Release notes](https://github.com/huggingface/optimum/releases)
- [Commits](huggingface/optimum@v1.20.0...v1.21.2)

---
updated-dependencies:
- dependency-name: optimum[openvino]
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

samples/requirements.txt

@@ -1,4 +1,4 @@
 --extra-index-url https://download.pytorch.org/whl/cpu
-optimum[openvino]==1.20.0
+optimum[openvino]==1.21.2
 einops==0.8.0  # For Qwen
 transformers_stream_generator==0.0.5  # For Qwen