flepimop patch unit test for seir::parameters

Added a unit test to demonstrate the issue described in
#375 (comment)
with respect to the `seir::parameters` section. Appears to be related to
if the parameters are a list or a dict.

flepimop/gempyor_pkg/tests/cli/test_flepimop_patch_cli.py

@@ -0,0 +1,76 @@
+from pathlib import Path
+from typing import Any
+
+from click.testing import CliRunner
+import pytest
+import yaml
+
+from gempyor.cli import patch
+
+
+@pytest.mark.parametrize(
+    ("data_one", "data_two", "expected_parameters"),
+    (
+        (
+            {
+                "seir": {
+                    "parameters": {
+                        "beta": {"value": 1.2},
+                    }
+                }
+            },
+            {
+                "seir": {
+                    "parameters": {
+                        "gamma": {"value": 3.4},
+                    }
+                }
+            },
+            {"gamma": {"value": 3.4}},
+        ),
+        (
+            {
+                "seir": {
+                    "parameters": {
+                        "sigma": {"value": 5.6},
+                        "gamma": {"value": 7.8},
+                    }
+                }
+            },
+            {
+                "seir": {
+                    "parameters": {
+                        "gamma": {"value": 3.4},
+                    }
+                }
+            },
+            {"gamma": {"value": 3.4}},
+        ),
+    ),
+)
+def test_patch_seir_parameters_behavior(
+    tmp_path: Path,
+    monkeypatch: pytest.MonkeyPatch,
+    data_one: dict[str, Any],
+    data_two: dict[str, Any],
+    expected_parameters: dict[str, Any],
+) -> None:
+    # Setup the test
+    monkeypatch.chdir(tmp_path)
+    config_one = tmp_path / "config_one.yml"
+    config_one.write_text(yaml.dump(data_one))
+    config_two = tmp_path / "config_two.yml"
+    config_two.write_text(yaml.dump(data_two))
+
+    # Invoke the command
+    runner = CliRunner()
+    with pytest.warns(
+        UserWarning, match="^Configuration files contain overlapping keys: {'seir'}.$"
+    ):
+        result = runner.invoke(patch, [config_one.name, config_two.name])
+    assert result.exit_code == 0
+
+    # Check the output
+    patched_config = yaml.safe_load(result.output)
+    assert "seir" in patched_config
+    assert patched_config["seir"]["parameters"] == expected_parameters