Replace gym to gymnasium in reinforcement learning tutorial (#981)

In this PR, I replace the deprecated OpenAI Gym library with its
successor, [Gymnasium](https://gymnasium.farama.org/index.html).
The changes target the notebooks used for the reinforcement learning
tutorials, and the corresponding CI configurations have been updated
accordingly. I also verified that the execution results remain
consistent with those obtained using the previous Gym library.

Author: kenya-sk

.github/workflows/ci-nightly-build-test.yaml

@@ -133,7 +133,7 @@ jobs:
           pip install jupyter
           pip install nbclient==0.6.5 jupyter-client==6.1.12 ipython==7.22.0
           pip install ipykernel==5.1.1
-          pip install gym==0.24.1
+          pip install gymnasium[classic-control]==1.2.3
           pip install seaborn==0.12.0
           pip install -q git+https://github.com/tensorflow/docs
           cd ..