chore(examples): change debian image version in gcp example

[kei01234kei]

Description

Changed image from debian-cloud/debian-9 to debian-cloud/debian-12 because debian-cloud/debian-9 image is not available.

➜  terraform-cdk git:(fix/machine_image) gcloud compute images list | grep debian
debian-10-buster-v20231010                            debian-cloud         debian-10                                      READY
debian-11-bullseye-arm64-v20231010                    debian-cloud         debian-11-arm64                                READY
debian-11-bullseye-v20231010                          debian-cloud         debian-11                                      READY
debian-12-bookworm-arm64-v20231010                    debian-cloud         debian-12-arm64                                READY
debian-12-bookworm-v20231010                          debian-cloud         debian-12                                      READY

Checklist

• I have updated the PR title to match CDKTF's style guide
• I have run the linter on my code locally
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation if applicable
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works if applicable
• New and existing unit tests pass locally with my changes

[hashicorp-cla]

All committers have signed the CLA.

[github-actions]

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