chore(deps): update ubuntu:22.04 docker digest to 3d256b4 (#353)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

discourse_rock/rockcraft.yaml

@@ -5,7 +5,7 @@ name: discourse
 summary: Discourse rock
 description: Discourse OCI image for the Discourse charm
 base: [email protected]
-# renovate: base: ubuntu:22.04@sha256:3c61d3759c2639d4b836d32a2d3c83fa0214e36f195a3421018dbaaf79cbe37f
+# renovate: base: ubuntu:22.04@sha256:3d256b40acbf7859ab80126ea5dca7527b6f72d2288cbd90be1369cc10fa9dfc
 run-user: _daemon_  # UID/GID 584792
 license: Apache-2.0
 version: "1.0"