[TEMP - do not merge] Force PR validation to test Python 3.15

Temporary commit to exercise the 3.15 conda-forge validation path on this PR:
- generate_binary_build_matrix.py: nightly python arches -> [3.15, 3.15t]
  (PR limit picks the first, so the PR validates 3.15 across linux arches).
- validate-nightly-binaries.yml: scope to os=linux and torchonly=true
  (no torchvision cp315 wheels yet).

REVERT THIS COMMIT before merging #8216.

Author: atalman

.github/workflows/validate-linux-binaries.yml

@@ -106,7 +106,9 @@ jobs:
       package-type: wheel,libtorch
       os: linux
       channel: ${{ inputs.channel }}
-      test-infra-ref: release/2.13
+      # TEMPORARY (revert before merge): use the PR branch so the matrix is
+      # generated by this PR's generate_binary_build_matrix.py (3.15/3.15t).
+      test-infra-ref: fix-py315-condaforge-pytorch-ref-release-2.13
       use-only-dl-pytorch-org: ${{ inputs.use-only-dl-pytorch-org }}
       with-xpu: enable
 
@@ -121,6 +123,9 @@ jobs:
       runner: ${{ matrix.validation_runner }}
       repository: "pytorch/pytorch"
       ref: release/2.13
+      # TEMPORARY (revert before merge): use the PR branch so validate_binaries.sh
+      # (with the Python 3.15 conda-forge setup) comes from this PR.
+      test-infra-ref: fix-py315-condaforge-pytorch-ref-release-2.13
       job-name: ${{ matrix.build_name }}
       docker-image: ${{ ((matrix.gpu_arch_type == 'xpu' || matrix.gpu_arch_type == 'rocm') && matrix.container_image) || 'pytorch/almalinux-builder:cpu-main' }}
       binary-matrix: ${{ toJSON(matrix) }}

.github/workflows/validate-nightly-binaries.yml

@@ -32,4 +32,7 @@ jobs:
     uses: ./.github/workflows/validate-binaries.yml
     with:
       channel: nightly
-      os: all
+      # TEMPORARY (revert before merge): scope to linux and torch-only to test
+      # the Python 3.15 validation path (no torchvision cp315 wheels yet).
+      os: linux
+      torchonly: true

tools/scripts/generate_binary_build_matrix.py

@@ -22,7 +22,9 @@
 
 
 PYTHON_ARCHES_DICT = {
-    "nightly": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"],
+    # TEMPORARY (revert before merge): restrict nightly to 3.15/3.15t so this
+    # PR's nightly validation exercises the Python 3.15 conda-forge setup.
+    "nightly": ["3.15", "3.15t"],
     "test": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"],
     "release": ["3.10", "3.11", "3.12", "3.13", "3.14", "3.14t"],
 }