cloudbuild: bump timeout to 3600s

The cloud-provider-aws-push-images postsubmit has been running up
against the 1200s (20 min) Cloud Build timeout:

- The new gcb-docker-gcloud image (pinned in #1399) is larger and
  pushes/pulls take slightly longer, and GCB's shared pool has been
  slower overall, so step 1 (multi-arch buildx) routinely now uses
  16-19 of the 20 available minutes.
- Step 2 (cloudbuild-artifacts) then has almost no budget left and
  is killed mid-`hack/install-gsutil.sh`, which means the
  ecr-credential-provider binaries never reach
  gs://k8s-staging-provider-aws/releases/.

Observed failures after #1399 landed:
- release-1.36:
  https://prow.k8s.io/view/gs/kubernetes-ci-logs/logs/cloud-provider-aws-push-images/2051718180123971584
  (step 1 ok, step 2 TIMEOUT installing gsutil)
- master:
  https://prow.k8s.io/view/gs/kubernetes-ci-logs/logs/cloud-provider-aws-push-images/2051514822092132352
  (step 1 buildkit session deadline during registry push)

Cross-check: the last successful binary upload to the staging
releases bucket was v1.35.1-5-g7dac1f6 on 2026-03-27 — step 2 has
effectively been timing out for over a month, independent of the
image pin issue.

Bumping the overall build timeout to 3600s (60 min) gives headroom
for GCB variability, keeps step 1 multi-arch pushes reliable, and
leaves enough budget for the existing install-gsutil + upload flow.
A follow-up PR can skip the SDK reinstall by switching the step 2
base image.

Signed-off-by: Ganesh Putta <ganiredi@amazon.com>

Author: Ganiredi

cloudbuild.yaml

@@ -30,4 +30,4 @@ substitutions:
   # Remove date prefix (first 10 characters) to create valid semver version:
   # v20220510-v1.24.0-alpha.0-15-g09bd268 => v1.24.0-alpha.0-15-g09bd268
   _SHORT_TAG: '${_GIT_TAG:10}'
-timeout: 1200s
+timeout: 3600s