CI: enable AVX2 build

Author: mshabunin

.github/workflows/PR-4.x.yaml

@@ -24,6 +24,9 @@ jobs:
   Ubuntu2404-x64:
     uses: opencv/ci-gha-workflow/.github/workflows/OCV-PR-4.x-U24.yaml@main
 
+  Ubuntu2404-x64-AVX2:
+    uses: opencv/ci-gha-workflow/.github/workflows/OCV-PR-4.x-U24-AVX2.yaml@main
+
   Ubuntu2004-x64-CUDA:
     if: "${{ contains(github.event.pull_request.labels.*.name, 'category: dnn') }} || ${{ contains(github.event.pull_request.labels.*.name, 'category: dnn (onnx)') }}"
     uses: opencv/ci-gha-workflow/.github/workflows/OCV-PR-4.x-U20-Cuda.yaml@main