Set enctype to multipart/form-data for invoice status form

Since this form is “shared” with the “full” form, that now includes
files, it has to be multipart/form-data too.

web/template/invoices/index.gohtml

@@ -90,7 +90,8 @@
                     <td>
                         <details class="invoice-status menu">
                             <summary class="invoice-status-{{ .Status }}">{{ .StatusLabel }}</summary>
-                            <form action="{{companyURI "/invoices/"}}{{ .Slug }}" method="POST" data-hx-boost="true">
+                            <form action="{{companyURI "/invoices/"}}{{ .Slug }}" method="POST"
+                                  enctype="multipart/form-data" data-hx-boost="true">
                                 {{ csrfToken }}
                                 {{ putMethod }}
                                 <input type="hidden" name="quick" value="status">