Update examples_core_examples.rst

[che-shr-cat]

Just fixing a typo, as the LM is a decoder, not an encoder

Checklist

• [X] This PR fixes a minor issue (e.g.: typo or small bug) or improves the docs (you can dismiss the other checks if that's the case).
• [ ] This change is discussed in a Github issue/ discussion (please add a link).
• [ ] The documentation and docstrings adhere to the documentation guidelines.
• [ ] This change includes necessary high-coverage tests. (No quality testing = no merge!)