update sources to Ubuntu-5.0.0-25.26

(generated with debian/scripts/import-upstream-tag)

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

diff --git a/submodules/ubuntu-disco b/submodules/ubuntu-disco
index 4d012aad3e0866fe6cd1ca6030f6adbd171879ae..308b2ca8ec79c27597abb985621d037bbdad0028 160000 (submodule)
--- a/submodules/ubuntu-disco
+++ b/submodules/ubuntu-disco
@@ -1 +1 @@
-Subproject commit 4d012aad3e0866fe6cd1ca6030f6adbd171879ae
+Subproject commit 308b2ca8ec79c27597abb985621d037bbdad0028