build(deps): bump ubuntu in /tools/ubuntu-cross

Bumps ubuntu from `c35e29c` to `7a39814`.

---
updated-dependencies:
- dependency-name: ubuntu
  dependency-version: noble
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

tools/ubuntu-cross/Dockerfile

@@ -1,5 +1,5 @@
 FROM --platform=${BUILDPLATFORM} tonistiigi/xx:master@sha256:de6f2b4d9a2a7bb3c7df745e12be6b1b90380783b4084f84fd21aee8e6330ec1 AS xx
-FROM --platform=${BUILDPLATFORM} ubuntu:noble@sha256:c35e29c9450151419d9448b0fd75374fec4fff364a27f176fb458d472dfc9e54 AS build
+FROM --platform=${BUILDPLATFORM} ubuntu:noble@sha256:7a398144c5a2fa7dbd9362e460779dc6659bd9b19df50f724250c62ca7812eb3 AS build
 COPY --from=xx / /
 
 RUN <<EOF