lvm plugin: properly handle qcow2 format when querying volume size info

In particular this fixes moving a qcow2 on top of LVM to a different
storage.

Fixes: eda88c9 ("lvmplugin: add qcow2 snapshot")
Reported-by: Michael Köppl <m.koeppl@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Link: https://lore.proxmox.com/20250718102023.70591-1-f.ebner@proxmox.com

src/PVE/Storage/LVMPlugin.pm

@@ -930,8 +930,12 @@ sub volume_resize {
 
 sub volume_size_info {
     my ($class, $scfg, $storeid, $volname, $timeout) = @_;
+
+    my ($format) = ($class->parse_volname($volname))[6];
     my $path = $class->filesystem_path($scfg, $volname);
 
+    return PVE::Storage::Plugin::file_size_info($path, $timeout, $format) if $format eq 'qcow2';
+
     my $cmd = [
         '/sbin/lvs',
         '--separator',