Fix: Allow subtraction of IdentityGate in PauliSum.__sub__

Author: RevanthGundala

cirq-core/cirq/ops/linear_combinations.py

@@ -798,7 +798,10 @@ def __isub__(self, other):
 
     def __sub__(self, other):
         if not isinstance(other, (numbers.Complex, PauliString, PauliSum)):
-            return NotImplemented
+            if hasattr(other, 'gate') and isinstance(other.gate, identity.IdentityGate):
+                other = PauliString(other)
+            else:
+                return NotImplemented
         result = self.copy()
         result -= other
         return result