[gnome-builder/wip/gtk4-port] plugins/project-tree: use margin instead of defuct border-width

[Christian Hergert <chergert src gnome org>]

commit 6d736788ead2efc28412a7916523db987fe2e426
Author: Christian Hergert <chergert redhat com>
Date:   Thu Apr 28 21:00:53 2022 -0700

    plugins/project-tree: use margin instead of defuct border-width

 src/plugins/project-tree/gbp-new-file-popover.ui | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/src/plugins/project-tree/gbp-new-file-popover.ui 
b/src/plugins/project-tree/gbp-new-file-popover.ui
index 5cbce4915..a4eacbb80 100644
--- a/src/plugins/project-tree/gbp-new-file-popover.ui
+++ b/src/plugins/project-tree/gbp-new-file-popover.ui
@@ -4,7 +4,10 @@
   <template class="GbpNewFilePopover" parent="GtkPopover">
     <child>
       <object class="GtkBox">
-        <property name="border-width">12</property>
+        <property name="margin-top">12</property>
+        <property name="margin-bottom">12</property>
+        <property name="margin-start">12</property>
+        <property name="margin-end">12</property>
         <property name="orientation">vertical</property>
         <property name="spacing">6</property>
         <property name="visible">true</property>