docs: コードブロックのファイル名が表示されない問題の修正

[m1sk9]

Details of implementation (実施内容)

• 知らぬ間?に Nextra のコードブロックで使用できるファイル名のプロパティ名が filename に変わっており、表示できていなかったのでそれらを修正しました。

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[codecov]

Codecov Report

Merging #954 (b9796e1) into main (05eba26) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #954   +/-   ##
=======================================
  Coverage   74.16%   74.16%           
=======================================
  Files          72       72           
  Lines        4915     4915           
  Branches      419      419           
=======================================
  Hits         3645     3645           
  Misses        852      852           
  Partials      418      418           

Flag	Coverage Δ
unittests	74.16% <ø> (ø)

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