Set ensemble name of single test run to "ensemble"

No reason to use date as name.
Makes writing tests easier.

src/ert/gui/simulation/single_test_run_panel.py

@@ -1,5 +1,4 @@
 from dataclasses import dataclass
-from datetime import datetime
 
 from qtpy import QtCore
 from qtpy.QtWidgets import QFormLayout, QLabel
@@ -37,5 +36,4 @@ def __init__(self, run_path: str, notifier: ErtNotifier):
         self.setLayout(layout)
 
     def get_experiment_arguments(self) -> Arguments:
-        ensemble_name = f"{datetime.now().strftime('%Y-%m-%dT%H%M')}"
-        return Arguments(TEST_RUN_MODE, ensemble_name, "single_test_run")
+        return Arguments(TEST_RUN_MODE, "ensemble", "single_test_run")

tests/unit_tests/gui/test_single_test_run.py

@@ -1,6 +1,5 @@
 import contextlib
 import shutil
-from datetime import datetime
 
 from qtpy.QtCore import Qt
 from qtpy.QtWidgets import (
@@ -38,4 +37,7 @@ def test_single_test_run_after_ensemble_experiment(
 
     storage = gui.notifier.storage
     assert "single_test_run" in [exp.name for exp in storage.experiments]
-    assert any(str(datetime.now().year) in ens.name for ens in storage.ensembles)
+    ensemble_names = [ens.name for ens in storage.ensembles]
+    assert "iter-0" in ensemble_names
+    # Default ensemble name when running single test run
+    assert "ensemble" in ensemble_names