Add tallies to eigenvalue_genperbatch test

tests/regression_tests/eigenvalue_genperbatch/inputs_true.dat

@@ -23,3 +23,9 @@
     </space>
   </source>
 </settings>
+<?xml version='1.0' encoding='utf-8'?>
+<tallies>
+  <tally id="1">
+    <scores>flux</scores>
+  </tally>
+</tallies>

tests/regression_tests/eigenvalue_genperbatch/results_true.dat

@@ -1,2 +1,5 @@
 k-combined:
 3.001411E-01 2.669758E-03
+tally 1:
+3.219698E+01
+2.591699E+02

tests/regression_tests/eigenvalue_genperbatch/test.py

@@ -24,6 +24,10 @@ def model():
     space = openmc.stats.Box((-4.0, -4.0, -4.0), (4.0, 4.0, 4.))
     model.settings.source = openmc.Source(space=space)
 
+    t = openmc.Tally()
+    t.scores = ['flux']
+    model.tallies.append(t)
+
     return model