Minor style fix in sanity.py

Author: vkarak

reframe/utility/sanity.py

@@ -487,16 +487,16 @@ def assert_reference(val, ref, lower_thres=None, upper_thres=None, msg=None):
         try:
             evaluate(assert_bounded(lower_thres, lower_thres_limit, 0))
         except SanityError:
-            raise SanityError('invalid low threshold value: %s'
-                              % lower_thres) from None
+            raise SanityError('invalid low threshold value: %s' %
+                              lower_thres) from None
 
     if upper_thres is not None:
         upper_thres_limit = None if ref >= 0 else 1
         try:
             evaluate(assert_bounded(upper_thres, 0, upper_thres_limit))
         except SanityError:
-            raise SanityError('invalid high threshold value: %s'
-                              % upper_thres) from None
+            raise SanityError('invalid high threshold value: %s' %
+                              upper_thres) from None
 
     def calc_bound(thres):
         if thres is None: