Refactor conditional logic in _isclose function for better clarity

Signed-off-by: Leandro Augusto Lacerda Campos <15185896+leandrolcampos@users.noreply.github.com>

stdlib/src/testing/testing.mojo

@@ -50,7 +50,7 @@ fn _isclose(
     if a.type.is_bool() or a.type.is_integral():
         return a == b
     else:
-        var both_nan = (isnan(a) & isnan(b))
+        var both_nan = isnan(a) & isnan(b)
         if equal_nan and both_nan.reduce_and():
             return True
 
@@ -63,10 +63,7 @@ fn _isclose(
             & (_abs(a - b) <= (atol_vec.max(rtol_vec * _abs(a).max(_abs(b)))))
         )
 
-        if not equal_nan:
-            return res
-
-        return res | both_nan
+        return res | both_nan if equal_nan else res
 
 
 # ===----------------------------------------------------------------------=== #