Update training_jetbot_reward_exploration.rst

[dougfulop]

tiny doc formatting issue

Description

Just fixed a doc formatting issue (an extra space prevents proper syntax highlighting on this documentation page)

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Screenshots

Please attach before and after screenshots of the change if applicable.

Checklist

• I have run the pre-commit checks with ./isaaclab.sh --format
• [ x] I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there