fix(ci): Use absolute path for PYTHONPATH in upload docs workflow

The upload-adk-docs-to-vertex-ai-search workflow failed with ModuleNotFoundError: No module named 'adk_answering_agent' because the relative PYTHONPATH path did not resolve correctly under some CI environment execution states. Resolved by using the absolute ${{ github.workspace }} path.

Change-Id: I18c72b671f33c134bd08601b4a97671a1b1b0fa9

Author: xuanyang15

.github/workflows/upload-adk-docs-to-vertex-ai-search.yml

@@ -51,5 +51,5 @@ jobs:
           GCS_BUCKET_NAME: ${{ secrets.GCS_BUCKET_NAME }}
           ADK_DOCS_ROOT_PATH: /tmp/adk-docs
           ADK_PYTHON_ROOT_PATH: /tmp/adk-python
-          PYTHONPATH: contributing/samples/adk_team
+          PYTHONPATH: ${{ github.workspace }}/contributing/samples/adk_team
         run: python -m adk_answering_agent.upload_docs_to_vertex_ai_search