[CI] Move s390 binary build to its own workflow (#137304)

It was added by https://github.com/pytorch/pytorch/pull/125399 and takes 3 hours to finish
Considering limited number of runners, it often causes queueing see:
<img width="402" alt="image" src="https://github.com/user-attachments/assets/5c67c1d6-af4c-4453-a089-aa1174513bfa">

Pull Request resolved: https://github.com/pytorch/pytorch/pull/137304
Approved by: https://github.com/kit1980, https://github.com/huydhn, https://github.com/atalman

.github/pytorch-probot.yml

@@ -16,6 +16,7 @@ ciflow_push_tags:
 - ciflow/nightly
 - ciflow/periodic
 - ciflow/rocm
+- ciflow/s390
 - ciflow/slow
 - ciflow/trunk
 - ciflow/unstable

.github/workflows/s390.yml

@@ -0,0 +1,24 @@
+name: s390
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - ciflow/s390/*
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref_name }}-${{ github.ref_type == 'branch' && github.sha }}-${{ github.event_name == 'workflow_dispatch' }}-${{ github.event_name == 'schedule' }}
+  cancel-in-progress: true
+
+permissions: read-all
+
+jobs:
+  linux-manylinux-2_28-py3-cpu-s390x-build:
+    name: linux-manylinux-2_28-py3-cpu-s390x
+    uses: ./.github/workflows/_linux-build.yml
+    with:
+      build-environment: linux-s390x-binary-manywheel
+      docker-image-name: pytorch/manylinuxs390x-builder:cpu-s390x-main
+      runner: linux.s390x

.github/workflows/trunk.yml

@@ -316,11 +316,3 @@ jobs:
       build-environment: linux-focal-cuda11.8-py3.10-gcc9-experimental-split-build
       docker-image: ${{ needs.linux-focal-cuda11_8-py3_10-gcc9-experimental-split-build.outputs.docker-image }}
       test-matrix: ${{ needs.linux-focal-cuda11_8-py3_10-gcc9-experimental-split-build.outputs.test-matrix }}
-
-  linux-manylinux-2_28-py3-cpu-s390x-build:
-    name: linux-manylinux-2_28-py3-cpu-s390x
-    uses: ./.github/workflows/_linux-build.yml
-    with:
-      build-environment: linux-s390x-binary-manywheel
-      docker-image-name: pytorch/manylinuxs390x-builder:cpu-s390x-main
-      runner: linux.s390x