fix(tests): add missing Behave step definitions for pyyaml_security Scenario 2

Scenario 2 in features/pyyaml_security.feature referenced three step
definitions that were not implemented in the step file, causing
StepDefinitionNotFoundError and CI unit_tests failure:

- When I call load_yaml_text with YAML text "..."
- Then the load_yaml_text result should have key "..." equal to "..."

Added both missing step definitions with proper type annotations.
Also fixed dead code (except (ValueError, Exception) -> except Exception,
ruff B014) and toned down the alarmist assertion message per reviewer
feedback.

features/steps/pyyaml_security_steps.py

@@ -8,6 +8,7 @@ code execution (CVE-2017-18342 mitigation, issue #9055).
 from __future__ import annotations
 
 from importlib.metadata import version as pkg_version
+from typing import Any
 
 from behave import given, then, when  # type: ignore[import-untyped]
 from behave.runner import Context  # type: ignore[import-untyped]
@@ -50,6 +51,30 @@ def step_assert_pyyaml_version(context: Context) -> None:
 # ── yaml_loader safe_load enforcement ───────────────────────────────
 
 
+@when('I call load_yaml_text with YAML text "{yaml_text}"')
+def step_load_yaml_text(context: Context, yaml_text: str) -> None:
+    """Call load_yaml_text with the given YAML text and store the result.
+
+    The YAML text is passed as a quoted string in the step, with ``\\n``
+    escape sequences representing literal newlines.
+    """
+    normalised = yaml_text.replace("\\n", "\n")
+    context.load_yaml_result: dict[str, Any] = load_yaml_text(normalised)
+
+
+@then('the load_yaml_text result should have key "{key}" equal to "{value}"')
+def step_assert_yaml_result_key(context: Context, key: str, value: str) -> None:
+    """Assert that the parsed YAML result contains the expected key/value pair."""
+    result: dict[str, Any] = context.load_yaml_result
+    assert key in result, (
+        f"Expected key '{key}' in load_yaml_text result, but it was not found. "
+        f"Actual keys: {list(result.keys())}"
+    )
+    assert result[key] == value, (
+        f"Expected result['{key}'] == '{value}', but got '{result[key]}'."
+    )
+
+
 @when("I call load_yaml_text with unsafe YAML containing a Python object tag")
 def step_load_unsafe_yaml(context: Context) -> None:
     """Attempt to load YAML with a Python object constructor tag.
@@ -62,7 +87,7 @@ def step_load_unsafe_yaml(context: Context) -> None:
     unsafe_yaml = "!!python/object/apply:os.system ['echo pwned']"
     try:
         load_yaml_text(unsafe_yaml)
-    except (ValueError, Exception) as exc:
+    except Exception as exc:
         context.caught_error = exc
 
 
@@ -71,6 +96,5 @@ def step_assert_value_error_raised(context: Context) -> None:
     """Assert that an error was raised when loading unsafe YAML."""
     assert context.caught_error is not None, (
         "Expected an error when loading YAML with Python object tags, "
-        "but none was raised. This indicates yaml.load() with an unsafe "
-        "Loader may be in use — a critical security vulnerability."
+        "but none was raised. This may indicate unsafe YAML loading is in use."
     )