fix: mock CUDA virtual package in GPU-less CI for pixi >= 0.76

.github/workflows/ci.yml.jinja

@@ -1,10 +1,18 @@
+{%- set effective_cuda_version = cuda_version if pytorch_cuda_preset == 'custom' else pytorch_cuda_preset.split('-cuda-')[1] -%}
 name: CI
 
 on:
   push:
     branches: [main]
   pull_request:
     branches: [main]
+{%- if package_manager == "pixi" %}
+
+env:
+  # GPU-less runners cannot satisfy the cuda system-requirement;
+  # pixi >= 0.76 refuses to solve without this mock.
+  CONDA_OVERRIDE_CUDA: "{{ effective_cuda_version }}"
+{%- endif %}
 
 jobs:
 {%- if use_ruff or use_ty %}

.github/workflows/test-template.yml

@@ -6,6 +6,12 @@ on:
   pull_request:
   workflow_dispatch:
 
+env:
+  # GPU-less runners cannot satisfy the generated project's cuda
+  # system-requirement; pixi >= 0.76 refuses to solve without this mock.
+  # Keep in sync with the CUDA version of the matrix pytorch-presets.
+  CONDA_OVERRIDE_CUDA: "12.6"
+
 jobs:
   test-generation:
     name: Test Template Generation

.github/workflows/test.yml.jinja

@@ -1,10 +1,18 @@
+{%- set effective_cuda_version = cuda_version if pytorch_cuda_preset == 'custom' else pytorch_cuda_preset.split('-cuda-')[1] -%}
 name: Tests
 
 on:
   push:
     branches: [main]
   pull_request:
     branches: [main]
+{%- if package_manager == "pixi" %}
+
+env:
+  # GPU-less runners cannot satisfy the cuda system-requirement;
+  # pixi >= 0.76 refuses to solve without this mock.
+  CONDA_OVERRIDE_CUDA: "{{ effective_cuda_version }}"
+{%- endif %}
 
 jobs:
 {%- if use_pytest %}