gha: use vllm v0.6.1 for testing

[dtrifiro]

• use vLLM v0.6.1 tag
• fix linter complaints
• add missing oneDNN build dependency ([Hardware][Intel] Support compressed-tensor W8A8 for CPU backend vllm-project/vllm#7257)
• add missing openCL dependency

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.64%. Comparing base (51989ed) to head (e7a492d).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #125   +/-   ##
=======================================
  Coverage   55.64%   55.64%           
=======================================
  Files          24       24           
  Lines        1488     1488           
  Branches      269      269           
=======================================
  Hits          828      828           
  Misses        583      583           
  Partials       77       77           

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