Fix bug where duplicate dates in summary caused update to crash

We drop all duplicate time steps from the summary dates, and only
read the first one.

src/ert/config/summary_config.py

@@ -60,6 +60,7 @@ def read_from_file(self, run_path: str, iens: int) -> xr.Dataset:
         data = []
         keys = []
         time_map = summary.alloc_time_vector(True)
+        time_map.selectUnique()
         axis = [t.datetime() for t in time_map]
         if self.refcase:
             existing_time_map = self.refcase.alloc_time_vector(True)

tests/unit_tests/scenarios/test_summary_response.py

@@ -140,6 +140,27 @@ def test_that_different_length_is_ok_as_long_as_observation_time_exists(
     es_update.smootherUpdate(prior_ensemble, target_ensemble, "an id")
 
 
+def test_that_duplicate_summary_time_steps_does_not_fail(
+        setup_configuration,
+        prior_ensemble,
+        target_ensemble,
+):
+    ert = setup_configuration
+    ert.sample_prior(prior_ensemble, list(range(ert.getEnsembleSize())))
+    response_times = [
+        [datetime(2014, 9, 9)],
+        [datetime(2014, 9, 9)],
+        [datetime(2014, 9, 9), datetime(2014, 9, 9)],
+        [datetime(2014, 9, 9)],
+        [datetime(2014, 9, 9), datetime(1988, 9, 9)],
+    ]
+    create_responses(ert, prior_ensemble, response_times)
+
+    es_update = ESUpdate(ert)
+
+    es_update.smootherUpdate(prior_ensemble, target_ensemble, "an id")
+
+
 def run_sim(dates, value, fname="ECLIPSE_CASE"):
     """
     Create a summary file, the contents of which are not important