Bug#1118780: gtk4: Mipmap tests fail 16/32-bit pixel format conversions due to memory alignment issues

[Gregor Riepl]

> I have tested your patch now and it seems it just reduced the number of failures by one.
I tested the patch from https://gitlab.gnome.org/GNOME/gtk/-/issues/7801#note_2586231 and can confirm that it does the trick.

Please use this instead of my patch:

diff --git a/testsuite/gdk/gdktestutils.c b/testsuite/gdk/gdktestutils.c
index 91ec99af5e..02e901bf37 100644
--- a/testsuite/gdk/gdktestutils.c
+++ b/testsuite/gdk/gdktestutils.c
@@ -658,8 +658,11 @@ texture_builder_init (TextureBuilder  *builder,
                        int              width,
                        int              height)
  {
-  gdk_memory_layout_init (&builder->layout, format, width, height, 1);
-  gdk_memory_layout_fudge (&builder->layout, 1);
+  gsize align;
+
+  align = gdk_memory_format_alignment (format);
+  gdk_memory_layout_init (&builder->layout, format, width, height, align);
+  gdk_memory_layout_fudge (&builder->layout, align);
    builder->pixels = g_malloc0 (builder->layout.size);
  }