Update solve docstring with new callback syntax

[Vaibhavdixit02]

Checklist

• [ ] Appropriate tests were added
• [ ] Any code changes were done in a way that does not break public API
• [ ] All documentation related to code changes were updated
• [ ] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [ ] Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (d5edf1f) 27.13% compared to head (d86463b) 30.37%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #590 +/- ## ========================================== + Coverage 27.13% 30.37% +3.24% ========================================== Files 53 53 Lines 4032 4039 +7 ========================================== + Hits 1094 1227 +133 + Misses 2938 2812 -126 ```

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