fix: use .ts extension for generated index

[gregberge]

Fix #462

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[codecov]

Codecov Report

Merging #670 (fdb2d64) into main (c57ee04) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #670   +/-   ##
=======================================
  Coverage   92.45%   92.45%           
=======================================
  Files          32       32           
  Lines         729      729           
  Branches      240      240           
=======================================
  Hits          674      674           
  Misses         53       53           
  Partials        2        2           

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