fix(web/teacher): fix create shift dialog

[taba2424]

やったこと

シフト作成ダイアログにて、 h4 タグの付与箇所が誤っていたので修正しました。
併せて、期間指定の入力フォームのUIの微調整 ( ~ の位置を中央寄せ) にする修正もしています。

レビュー時のポイント

残タスク

備考

[codecov]

Codecov Report

Merging #197 (3b4d9bf) into main (2b04c00) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #197   +/-   ##
=======================================
  Coverage   82.61%   82.61%           
=======================================
  Files         179      179           
  Lines        7016     7016           
  Branches      133      133           
=======================================
  Hits         5796     5796           
  Misses       1124     1124           
  Partials       96       96           

Flag	Coverage Δ
student-web	65.17% <ø> (ø)
teacher-web	58.69% <ø> (ø)

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

Impacted Files	Coverage Δ
...cher/src/components/organisms/TheShiftEditCard.vue	100.00% <ø> (ø)
...acher/src/components/organisms/TheShiftNewCard.vue	100.00% <ø> (ø)