qemu_driver: Fix virDomainSaveImageDefineXML

Commit 28a06215 added support to restore
sparse images but changed the boolean that controls if we open the file
as read-only or read-write. Editing XML in the save image resulted in
following error message:

    failed to write header to domain save file '/data/images/fedora40.save': Bad file descriptor

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Jim Fehlig <jfehlig@suse.com>

src/qemu/qemu_driver.c

@@ -5948,7 +5948,7 @@ qemuDomainSaveImageDefineXML(virConnectPtr conn, const char *path,
     if (qemuSaveImageGetMetadata(driver, NULL, path, &def, &data) < 0)
         goto cleanup;
-    fd = qemuSaveImageOpen(driver, path, false, false, NULL, false);
+    fd = qemuSaveImageOpen(driver, path, false, false, NULL, true);
     if (fd < 0)
         goto cleanup;