Fix test to use frs fixture and enum key strings

Author: nikhilwoodruff

policyengine_uk_data/tests/test_highest_education.py

@@ -1,5 +1,9 @@
-def test_highest_education(baseline):
-    values = baseline.calculate("highest_education", period=2025)
-    assert "Tertiary" in set(values)
-    assert "Lower Secondary" in set(values)
-    assert "Upper Secondary" in set(values)
+from policyengine_uk import Microsimulation
+
+
+def test_highest_education(frs):
+    sim = Microsimulation(dataset=frs)
+    values = sim.calculate("highest_education", period=2025)
+    assert "TERTIARY" in set(values)
+    assert "LOWER_SECONDARY" in set(values)
+    assert "UPPER_SECONDARY" in set(values)