fix: handle type tracer correctly in indexed option array flattening

[lgray]

Fixes #3324

@pfackeldey if my little patch breaks things please give it a try. I'll try to cook up a test in the mean time.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.16%. Comparing base (b749e49) to head (781d502).
Report is 212 commits behind head on main.

Additional details and impacted files

Files with missing lines	Coverage Δ
src/awkward/contents/indexedoptionarray.py	88.61% <100.00%> (+0.39%)	⬆️

... and 161 files with indirect coverage changes

[lgray]

@jpivarski @pfackeldey this is now ready to go! the fix was that simple.

[jpivarski]

LGTM!

[jpivarski]

I think that GitHub Actions is having problems right now.

[lgray]

macos-12 images were sunset.

[lgray]

or was it supposed to automerge it?