chore(deps): upgrade PyYAML to address known security vulnerability

Remove 4 duplicate Behave step definitions from security_pyyaml_dependency_steps.py
that were causing AmbiguousStep errors (already defined in tdd_a2a_sdk_dependency_steps.py).

These duplicates caused CI / lint and CI / unit_tests to fail:
- @given('the pyproject.toml file exists at "{path}"') - duplicate
- @when('I read the project dependencies from pyproject.toml') - duplicate
- @when('I attempt to import the "{module_name}" module') - duplicate
- @then('the import should succeed without errors') - duplicate

Only 3 PyYAML-specific steps and 1 helper remain unique to this file.

ISSUES CLOSED: #9055

features/steps/security_pyyaml_dependency_steps.py

@@ -2,34 +2,16 @@
 
 from __future__ import annotations
 
-import importlib
 import re
 from pathlib import Path
 from typing import Any
 
 import tomllib
-from behave import given, then, when
+from behave import then, when
 from behave.runner import Context
 from packaging.version import Version
 
 
-@given('the pyproject.toml file exists at "{path}"')
-def step_pyproject_exists(context: Context, path: str) -> None:
-    """Verify pyproject.toml exists at the given path."""
-    repo_root = Path(__file__).parent.parent.parent  # features/steps -> repo root
-    pyproject_path = repo_root / path
-    assert pyproject_path.exists(), f"pyproject.toml not found at {path}"
-    context.pyproject_path = pyproject_path
-
-
-@when("I read the project dependencies from pyproject.toml")
-def step_read_project_dependencies(context: Context) -> None:
-    """Read the [project.dependencies] list from pyproject.toml."""
-    content = context.pyproject_path.read_bytes()
-    data: dict[str, Any] = _load_toml(content)
-    context.project_dependencies = data.get("project", {}).get("dependencies", [])
-
-
 @then('the dependency list should include a package matching "{pattern}"')
 def step_dependency_matches_pattern(context: Context, pattern: str) -> None:
     """Assert that a dependency in the project dependencies matches the given regex pattern."""
@@ -78,24 +60,6 @@ def step_pyyaml_minimum_version(context: Context, expected: str) -> None:
     )
 
 
-@when('I attempt to import the "{module_name}" module')
-def step_attempt_import(context: Context, module_name: str) -> None:
-    """Attempt to import the given module and record the result."""
-    try:
-        context.imported_module = importlib.import_module(module_name)
-        context.import_error = None
-    except ImportError as exc:
-        context.imported_module = None
-        context.import_error = exc
-
-
-@then("the import should succeed without errors")
-def step_import_succeeded(context: Context) -> None:
-    """Assert that the previous import attempt succeeded."""
-    assert context.import_error is None, f"Import failed with: {context.import_error}"
-    assert context.imported_module is not None, "Module was not imported"
-
-
 def _load_toml(content: bytes) -> dict[str, Any]:
     """Load a TOML file from bytes using the stdlib tomllib module (Python 3.11+)."""
     return tomllib.loads(content.decode("utf-8"))