Fix install page checkboxes and dropdown width (#30526)

Fixes: https://github.com/go-gitea/gitea/issues/30523

1. Fix checkbox rendering
2. Fix width of selection dropdowns (was too small)

---------

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Giteabot <teabot@gitea.io>
(cherry picked from commit 4f276a336355c4bf999034fb79f0fe5c967ceb50)

web_src/css/install.css

@@ -18,7 +18,8 @@
   width: auto;
 }
 
-.page-content.install form.ui.form input {
+.page-content.install form.ui.form input:not([type="checkbox"],[type="radio"]),
+.page-content.install form.ui.form .ui.selection.dropdown {
   width: 60%;
 }