Add btn-default class for file picker button

app/views/shared/_file_picker_button.html.haml

 - classes = local_assigns.fetch(:classes, '')
 
 %span.js-filepicker
-  %button.gl-button.btn.js-filepicker-button{ type: 'button', class: classes }= _("Choose file…")
+  %button.gl-button.btn.btn-default.js-filepicker-button{ type: 'button', class: classes }= _("Choose file…")
   %span.file_name.js-filepicker-filename= _("No file chosen.")
   = f.file_field field, class: "js-filepicker-input hidden"
   - if help_text.present?

changelogs/unreleased/btn-default-filepicker.yml

+---
+title: Add btn-default class for file picker button
+merge_request: 58238
+author: Yogi (@yo)
+type: changed