chore: bump langgraph version to 1.1.5 in CI and examples (#7435)

## Summary
- Bump `langgraph` version from `1.1.2` to `1.1.5` in the CI integration
test workflow version check
- Bump `langgraph` version from `1.1.2` to `1.1.5` in the prerelease
example `pyproject.toml` files

## Test plan
- [ ] CI integration tests pass with the updated version expectation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Will Fu-Hinthorn <will@langchain.dev>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

libs/cli/examples/graph_prerelease_reqs/deps/additional_deps/pyproject.toml

@@ -5,5 +5,5 @@ description = "Test for prerelease stuff"
 readme = "README.md"
 requires-python = ">=3.10"
 dependencies = [
-  "langgraph==1.1.2"
+  "langgraph==1.1.5"
 ]

libs/cli/examples/graph_prerelease_reqs/pyproject.toml

@@ -7,7 +7,7 @@ requires-python = ">=3.10"
 dependencies = [
   "langchain-openai==1.0.0a2",
   "langchain-anthropic==1.0.0a5",
-  "langgraph==1.1.2"
+  "langgraph==1.1.5"
 ]
 
 [tool.uv]