Add torchvision-extra-decoders build test (exercises 3.15 native build)

torchvision-extra-decoders is a torch C++ extension (CppExtension over
torch.utils.cpp_extension, install_requires=[], no torchvision needed), so
it's a good probe for whether the binary build path works on a new Python
such as 3.15/3.15t -- it actually compiles against libtorch for cp315
rather than just installing a pure-python package.

Mirrors meta-pytorch/torchvision-extra-decoders' linux_wheel.yaml: cpu-only
matrix, setup-py build, packaging/pre_build_script.sh (auditwheel +
conda libavif/libheif), post_build_script.sh, and the fake smoke test. On
PR CI the matrix is limited to 3.15/3.15t by the temporary force commit.

Author: atalman

.github/workflows/test_build_wheels_linux_extra_decoders.yml

@@ -0,0 +1,50 @@
+name: Test Build Linux Wheels torchvision-extra-decoders
+
+on:
+  pull_request:
+    paths:
+      - .github/actions/setup-binary-builds/action.yml
+      - .github/workflows/test_build_wheels_linux.yml
+      - .github/workflows/build_wheels_linux.yml
+      - .github/workflows/generate_binary_build_matrix.yml
+      - .github/workflows/test_build_wheels_linux_extra_decoders.yml
+      - tools/scripts/generate_binary_build_matrix.py
+      - tools/pkg-helpers/pytorch_pkg_helpers/version.py
+  workflow_dispatch:
+
+permissions:
+  id-token: write
+  contents: read
+
+jobs:
+  generate-matrix:
+    uses: ./.github/workflows/generate_binary_build_matrix.yml
+    with:
+      package-type: wheel
+      os: linux
+      test-infra-repository: ${{ github.repository }}
+      test-infra-ref: ${{ github.ref }}
+      with-cuda: disable
+      with-rocm: disable
+      with-xpu: disable
+      build-python-only: disable
+  test:
+    needs: generate-matrix
+    strategy:
+      fail-fast: false
+    # Build torchvision-extra-decoders (a torch C++ extension) to exercise the
+    # binary build path on new Python versions (e.g. 3.15 / 3.15t). Mirrors
+    # meta-pytorch/torchvision-extra-decoders/.github/workflows/linux_wheel.yaml.
+    uses: ./.github/workflows/build_wheels_linux.yml
+    name: torchvision-extra-decoders
+    with:
+      repository: meta-pytorch/torchvision-extra-decoders
+      ref: main
+      test-infra-repository: ${{ github.repository }}
+      test-infra-ref: ${{ github.ref }}
+      build-matrix: ${{ needs.generate-matrix.outputs.matrix }}
+      pre-script: packaging/pre_build_script.sh
+      post-script: packaging/post_build_script.sh
+      smoke-test-script: packaging/fake_smoke_test.py
+      package-name: torchvision_extra_decoders
+      trigger-event: "${{ github.event_name }}"