Steps used to produce this issue:
1. Create a content with revisions (Moderation) enabled.
2. Create more revisions by editing and saving fields.
3. Now choose any previous revision to revert and save.
4. Now edit the node and save again.
Now there will be message:
"The content has either been modified by another user, or you have already submitted modifications. As a result, your changes cannot be saved."
Solution
I found out that validation inside this in getting failed on reverting.
core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/EntityChangedConstraintValidator.php
So, I have update the Node time changed while reverting inside this file.
core/lib/Drupal/Core/Entity/Plugin/Validation/Constraint/EntityChangedConstraintValidator.php
Any suggestion and other ways are welcome. thanks.