chore(deps): bump transformers in /backend/python/coqui

Bumps [transformers](https://github.com/huggingface/transformers) from 4.48.3 to 5.8.1.
- [Release notes](https://github.com/huggingface/transformers/releases)
- [Commits](https://github.com/huggingface/transformers/compare/v4.48.3...v5.8.1)

---
updated-dependencies:
- dependency-name: transformers
  dependency-version: 5.8.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

backend/python/coqui/requirements-cpu.txt

@@ -1,5 +1,5 @@
 --extra-index-url https://download.pytorch.org/whl/cpu
-transformers==4.48.3
+transformers==5.8.1
 accelerate
 torch==2.4.1
 torchaudio==2.4.1

backend/python/coqui/requirements-cublas12.txt

@@ -1,5 +1,5 @@
 torch==2.4.1
 torchaudio==2.4.1
-transformers==4.48.3
+transformers==5.8.1
 accelerate
 coqui-tts

backend/python/coqui/requirements-hipblas.txt

@@ -1,6 +1,6 @@
 --extra-index-url https://download.pytorch.org/whl/rocm7.0
 torch==2.10.0+rocm7.0
 torchaudio==2.10.0+rocm7.0
-transformers==4.48.3
+transformers==5.8.1
 accelerate
 coqui-tts

backend/python/coqui/requirements-intel.txt

@@ -3,6 +3,6 @@ torch==2.8.0+xpu
 torchaudio==2.8.0+xpu
 optimum[openvino]
 setuptools
-transformers==4.48.3
+transformers==5.8.1
 accelerate
 coqui-tts

backend/python/coqui/requirements-mps.txt

@@ -1,4 +1,4 @@
 torch==2.7.1
-transformers==4.48.3
+transformers==5.8.1
 accelerate
 coqui-tts