chore(deps): bump ubuntu in /stack/build in the build-stack-images group

Bumps the build-stack-images group in /stack/build with 1 update: ubuntu.


Updates `ubuntu` from `b7f4819` to `3131b4c`

---
updated-dependencies:
- dependency-name: ubuntu
  dependency-version: '26.04'
  dependency-type: direct:production
  dependency-group: build-stack-images
...

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

Author: dependabot[bot]

stack/build/Dockerfile

@@ -2,7 +2,7 @@
 # Ubuntu 24.04 provides the full toolchain needed to compile Java apps
 # with the Paketo Java and Java Native Image buildpacks.
 
-FROM ubuntu:26.04@sha256:b7f48194d4d8b763a478a621cdc81c27be222ba2206ca3ca6bc42b49685f3d9e
+FROM ubuntu:26.04@sha256:3131b4cc82a783df6c9df078f86e01819a13594b865c2cad47bd1bca2b7063bb
 
 ARG CNB_USER_ID=1000
 ARG CNB_GROUP_ID=1000