consolidate Linux workflows on CPU and GPU

.github/unittest.sh

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+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Prepare conda
+CONDA_PATH=$(which conda)
+eval "$(${CONDA_PATH} shell.bash hook)"
+
+echo '::group::Set PyTorch conda channel and wheel index'
+# TODO: Can we maybe have this as environment variable in the job template? For example, `IS_RELEASE`.
+if [[ (${GITHUB_EVENT_NAME} = 'pull_request' && (${GITHUB_BASE_REF} = 'release'*)) || (${GITHUB_REF} = 'refs/heads/release'*) ]]; then
+  CHANNEL_ID=test
+else
+  CHANNEL_ID=nightly
+fi
+PYTORCH_CONDA_CHANNEL=pytorch-"${CHANNEL_ID}"
+echo "PYTORCH_CONDA_CHANNEL=${PYTORCH_CONDA_CHANNEL}"
+
+case $GPU_ARCH_TYPE in
+  cpu)
+    GPU_ARCH_ID="cpu"
+    ;;
+  cuda)
+    VERSION_WITHOUT_DOT=$(echo "${GPU_ARCH_VERSION}" | sed 's/\.//')
+    GPU_ARCH_ID="cu${VERSION_WITHOUT_DOT}"
+    ;;
+  *)
+    echo "Unknown GPU_ARCH_TYPE=${GPU_ARCH_TYPE}"
+    exit 1
+    ;;
+esac
+PYTORCH_WHEEL_INDEX="https://download.pytorch.org/whl/${CHANNEL_ID}/${GPU_ARCH_ID}"
+echo "PYTORCH_WHEEL_INDEX=${PYTORCH_WHEEL_INDEX}"
+echo '::endgroup::'
+
+echo '::group::Create build environment'
+conda create \
+  --name ci \
+  --quiet --yes \
+  python="${PYTHON_VERSION}" pip \
+  ninja libpng jpeg 'ffmpeg<4.3' \
+  -c "${PYTORCH_CONDA_CHANNEL}" \
+  -c conda-forge
+conda activate ci
+pip install --progress-bar=off --upgrade setuptools
+echo '::endgroup::'
+
+echo '::group::Install PyTorch'
+# Due to the supply chain attack in Dec 2022 (https://pytorch.org/blog/compromised-nightly-dependency/), we host all
+# third-party dependencies on Linux on our own indices and *don't* install them from PyPI.
+case "$(uname -s)" in
+    Linux*)
+      INDEX_TYPE="index-url"
+      ;;
+    *)
+      INDEX_TYPE="extra-index-url"
+esac
+
+pip install --progress-bar=off torch "--${INDEX_TYPE}=${PYTORCH_WHEEL_INDEX}"
+
+if [[ $GPU_ARCH_TYPE = 'cuda' ]]; then
+  python3 -c "import torch; exit(not torch.cuda.is_available())"
+fi
+echo '::endgroup::'
+
+echo '::group::Install TorchVision'
+python setup.py develop
+echo '::endgroup::'
+
+echo '::group::Collect PyTorch environment information'
+python -m torch.utils.collect_env
+echo '::endgroup::'
+
+echo '::group::Install testing utilities'
+pip install --progress-bar=off pytest pytest-mock pytest-cov
+echo '::endgroup::'
+
+echo '::group::Run tests'
+pytest --durations=25
+echo '::endgroup::'

.github/workflows/test-linux.yml

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+name: Unit-tests on Linux
+
+on:
+  pull_request:
+  push:
+    branches:
+      - nightly
+      - main
+      - release/*
+  workflow_dispatch:
+
+jobs:
+  tests:
+    strategy:
+      matrix:
+        python-version:
+          - "3.8"
+          - "3.9"
+          - "3.10"
+        runner: ["linux.12xlarge"]
+        gpu-arch-type: ["cpu"]
+        include:
+          - python-version: 3.8
+            runner: linux.g5.4xlarge.nvidia.gpu
+            gpu-arch-type: cuda
+            gpu-arch-version: "11.7"
+      fail-fast: false
+    uses: pytorch/test-infra/.github/workflows/linux_job.yml@main
+    with:
+      repository: pytorch/vision
+      runner: ${{ matrix.runner }}
+      gpu-arch-type: ${{ matrix.gpu-arch-type }}
+      gpu-arch-version: ${{ matrix.gpu-arch-version }}
+      timeout: 120
+      script: |
+        export PYTHON_VERSION=${{ matrix.python-version }}
+        export GPU_ARCH_TYPE=${{ matrix.gpu-arch-type }}
+        export GPU_ARCH_VERSION=${{ matrix.gpu-arch-version }}
+
+        ./.github/unittest.sh