Bump langchain-core from 1.0.3 to 1.2.28 in /samples/langgraph-sql-agent

Bumps [langchain-core](https://github.com/langchain-ai/langchain) from 1.0.3 to 1.2.28.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain-core==1.0.3...langchain-core==1.2.28)

---
updated-dependencies:
- dependency-name: langchain-core
  dependency-version: 1.2.28
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

samples/langgraph-sql-agent/requirements.txt

@@ -526,9 +526,9 @@ langchain-community==0.4.1 \
     --hash=sha256:2135abb2c7748a35c84613108f7ebf30f8505b18c3c18305ffaecfc7651f6c6a \
     --hash=sha256:f3b211832728ee89f169ddce8579b80a085222ddb4f4ed445a46e977d17b1e85
     # via langgraph-sql-agent
-langchain-core==1.0.3 \
-    --hash=sha256:10744945d21168fb40d1162a5f1cf69bf0137ff6ad2b12c87c199a5297410887 \
-    --hash=sha256:64f1bd45f04b174bbfd54c135a8adc52f4902b347c15a117d6383b412bf558a5
+langchain-core==1.2.28 \
+    --hash=sha256:271a3d8bd618f795fdeba112b0753980457fc90537c46a0c11998516a74dc2cb \
+    --hash=sha256:80764232581eaf8057bcefa71dbf8adc1f6a28d257ebd8b95ba9b8b452e8c6ac
     # via
     #   langchain-classic
     #   langchain-community