ci: split and use matrix to test containerd backed image store
follow-up https://github.com/moby/moby/pull/46402#pullrequestreview-1651587668

**- What I did**

Alternative to #46402 using a matrix and set required env vars to test containerd backed image store.

**- How I did it**

Sets a `storage` matrix conditionally based on `containerd-integration` GitHub label being set.

**- How to verify it**

**- Description for the changelog**
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Write a short (one line) summary that describes the changes in this
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**- A picture of a cute animal (not mandatory but encouraged)**


.github/workflows/windows-2019.yml
name: windows-2019

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

on:
  schedule:
    - cron: '0 10 * * *'
  workflow_dispatch:

jobs:
  validate-dco:
    uses: ./.github/workflows/.dco.yml

  run:
    needs:
      - validate-dco
    uses: ./.github/workflows/.windows.yml
    with:
      os: windows-2019
      send_coverage: false

name: windows-2019

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

on:
  schedule:
    - cron: '0 10 * * *'
  workflow_dispatch:

jobs:
  validate-dco:
    uses: ./.github/workflows/.dco.yml

  test-prepare:
    uses: ./.github/workflows/.test-prepare.yml
    needs:
      - validate-dco

  run:
    needs:
      - test-prepare
    uses: ./.github/workflows/.windows.yml
    strategy:
      fail-fast: false
      matrix:
        storage: ${{ fromJson(needs.test-prepare.outputs.matrix) }}
    with:
      os: windows-2019
      storage: ${{ matrix.storage }}
      send_coverage: false

Oh man