Fix: remove unsupported prompt-caching-scope-2026-01-05 header for vertex ai#20058

Sameerlite merged 1 commit intomainBerriAI/litellm:mainfrom

litellm_vertex_ai_prompt-caching-scope-2026-01-05,BerriAI/litellm:litellm_vertex_ai_prompt-caching-scope-2026-01-05,Copy head branch name to clipboard