fix: fix symbolic idxs interpolation for RODESolution

[AayushSabharwal]

Close #580

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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 40.84%. Comparing base (1624ee4) to head (d3c0827).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #673      +/-   ##
==========================================
+ Coverage   40.80%   40.84%   +0.04%     
==========================================
  Files          55       55              
  Lines        4490     4490              
==========================================
+ Hits         1832     1834       +2     
+ Misses       2658     2656       -2     

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