chore(infra): drop anthropic from core test matrix (#32146)

Stricter JSON schema validation broke a test. Test was fixed in
#32145. Core release runs
old tests (i.e., last released version of langchain-anthropic) against
new core. So we bypass anthropic for release. Will revert after.

Author: ccurme

.github/workflows/_release.yml

@@ -340,7 +340,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        partner: [openai, anthropic]
+        partner: [openai]
       fail-fast: false  # Continue testing other partners if one fails
     env:
       ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}