otelconf: plain was incorrectly using the wrong alias

[codeboten]

The underlying types were all the same, so this wasn't caught by the casting at the end of each func. Worth fixing to remove confusion.

Didn't add a changelog since the code in question isn't out yet.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.8%. Comparing base (183643f) to head (c936c16).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #8181   +/-   ##
=====================================
  Coverage   81.8%   81.8%           
=====================================
  Files        194     194           
  Lines      13377   13377           
=====================================
  Hits       10951   10951           
  Misses      2029    2029           
  Partials     397     397           

Files with missing lines	Coverage Δ
otelconf/config_json.go	92.9% <100.0%> (ø)

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