Do you still need a Test Plan when using CI/CD?
YES you do. Because a test plan will tell you at least the thing that you did not specify in your question: how often do you plan to run the tests? Which tests will run with which periodicity?
Maybe there is a common practice to do it every night. Is it feasible for your project? Which alternatives do you have? Why is one method better / worse than the other?
Which tests will be executed "continuously"? Top level / features-related? Architectural? Unit tests?
Can you test everything automatically? Does your system depend on other systems? How are the changes of the other systems managed and tested?
Even if "continuous" sounds so great, it is not at all continuous. At best, it is periodic. That is why you actually need to plan ahead.
Another question: what will happen when some test-case(s) fail? How will you handle the logging, reporting, monitoring, fixing?
Continuous vs. Periodic
A river flowing is continuous. Even if there is ice on the top of it. Testing cannot be continuous.
The code must achieve some certain "maturity" before it can be tested. The minimum pre-requisite is that it is compilable.
The minimum pre-requisite for delivery is that certain test-cases must pass. If they fail, the product is not safe for use.
A test-suite takes time. You do not execute everything at any point in time. It starts, and then it finishes, and then a new SW version is taken from the repository, and testing starts again, and ends again...
So such a system can be called "continuous" only if a lot of the practical details of reality are ignored - as it is usually done for marketing and advertising purposes.