ci(infra): expand integration tests dispatch dropdown to external partners (#37614)

Adds `aws`, `google-genai`, and `google-vertexai` to the manual-run
`working-directory` dropdown on the `⏰ Integration Tests` workflow.
These partners live in external repos (`langchain-ai/langchain-google`,
`langchain-ai/langchain-aws`) and were previously only reachable via the
free-form `working-directory-override` input despite the job already
checking them out into `libs/partners/`.

.github/workflows/integration_tests.yml

@@ -27,10 +27,13 @@ on:
           - "standard-tests"
           - "model-profiles"
           - "anthropic"
+          - "aws"
           - "chroma"
           - "deepseek"
           - "exa"
           - "fireworks"
+          - "google-genai"
+          - "google-vertexai"
           - "groq"
           - "huggingface"
           - "mistralai"