Merge bitcoin/bitcoin#35571: ci: use warp docker buildkit cache

b552f1713a ci: use warp docker buildkit cache (will)

Pull request description:

  This was inadvertently broken in #35441 when we dropped the runners job. Unfortunately GHA seems to continue just fine when this field is empty, so it wasn't noticed at runtime.

ACKs for top commit:
  m3dwards:
    ACK b552f1713a

Tree-SHA512: 0bc61b42e94b0a73ef6026dea3dce27fdea611218936e585b5232fde358b4fab4728d59338b86c75affec80c11b6f1fada56ffb785999fabae0b01becb41268d

.github/workflows/ci.yml

@@ -345,7 +345,7 @@ jobs:
       - name: Configure Docker
         uses: ./.github/actions/configure-docker
         with:
-          provider: ${{ needs.runners.outputs.provider }}
+          provider: ${{ github.repository == 'bitcoin/bitcoin' && 'warp' || 'gha' }}
 
       - name: CI script
         run: ./ci/test_run_all.sh
@@ -540,7 +540,7 @@ jobs:
       - name: Configure Docker
         uses: ./.github/actions/configure-docker
         with:
-          provider: ${{ matrix.provider || needs.runners.outputs.provider }}
+          provider: ${{ matrix.provider || (github.repository == 'bitcoin/bitcoin' && 'warp' || 'gha') }}
 
       - name: Clear unnecessary files
         if: ${{ github.repository != 'bitcoin/bitcoin' || matrix.provider == 'gha' }} # Only needed on GHA runners
@@ -584,7 +584,7 @@ jobs:
       - name: Configure Docker
         uses: ./.github/actions/configure-docker
         with:
-          provider: ${{ needs.runners.outputs.provider }}
+          provider: ${{ github.repository == 'bitcoin/bitcoin' && 'warp' || 'gha' }}
 
       - name: CI script
         run: |