GitHub Actions のミドルウェアバージョン修正

[nanasess]

• PHP8.1 を追加
• PHPStan のエラー修正

  Return type mixed of method php_user_filter_lf2crlf::filter() is not covariant with tentative return type int of method php_user_filter::filter().

• auto_detect_line_endings はPHP8.1.0以降非推奨

[codecov-commenter]

Codecov Report

Merging #524 (0add9ef) into master (4b76107) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #524   +/-   ##
=======================================
  Coverage   54.40%   54.40%           
=======================================
  Files          76       76           
  Lines        9039     9039           
=======================================
  Hits         4918     4918           
  Misses       4121     4121           

Flag	Coverage Δ
tests	54.40% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
data/class/SC_Initial.php	0.00% <0.00%> (ø)
data/class/helper/SC_Helper_CSV.php	0.00% <0.00%> (ø)

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[nanasess]

PHPStan のエラーは #522 で修正済み