Administration: Add primary class to the FTP credentials modal submit button.

This helps differentiate the two buttons available in the FTP credentials modal by setting a `primary` class to the submit button.

Props mapk, curdin, audrasjb, shailu25.
Fixes #37647.




git-svn-id: https://develop.svn.wordpress.org/trunk@58149 602fd350-edb4-49c9-b593-d223f7449a82

Author: audrasjb

src/wp-admin/includes/file.php

@@ -2664,7 +2664,7 @@ function request_filesystem_credentials( $form_post, $type = '', $error = false,
 	<p class="request-filesystem-credentials-action-buttons">
 		<?php wp_nonce_field( 'filesystem-credentials', '_fs_nonce', false, true ); ?>
 		<button class="button cancel-button" data-js-action="close" type="button"><?php _e( 'Cancel' ); ?></button>
-		<?php submit_button( __( 'Proceed' ), '', 'upgrade', false ); ?>
+		<?php submit_button( __( 'Proceed' ), 'primary', 'upgrade', false ); ?>
 	</p>
 </div>
 </form>