[CI] Update CI config to work with project

Pin the Python version to 3.11, since OpenAssetIO is currently
unavailable on PyPI for 3.12 (i.e. only currently supports VFX Reference
Platform CY23/24).

Checkout ComfyUI and add to PYTHONPATH for tests, since we make use of
its internal utility libraries. We also make use of some of the
dependencies of ComfyUI (e.g. numpy), so install ComfyUI's dependencies
into the environment.

Signed-off-by: David Feltell <david.feltell@foundry.com>

.github/workflows/build_pipeline.yml

@@ -6,21 +6,28 @@ name: CI build
 
 on:
   pull_request:
-    branches:
-      - master
-      - main
+  workflow_dispatch:
+
 jobs:
-  build:
+  test:
+    name: Test and Lint
     runs-on: ${{ matrix.os }}
     env:
       PYTHONIOENCODING: "utf8"
     strategy:
       matrix:
         os: [ ubuntu-latest ]
-        python-version: [ "3.12" ]
+        python-version: [ "3.11" ]
 
     steps:
       - uses: actions/checkout@v4
+
+      - uses: actions/checkout@v4
+        name: Checkout ComfyUI
+        with:
+          repository: comfyanonymous/ComfyUI
+          ref: v0.3.57
+          path: comfyui
       - name: Set up Python
         uses: actions/setup-python@v5
         with:
@@ -29,9 +36,12 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install .[dev]
-      - name: Run Linting
-        run: |
-          ruff check .
+          pip install -r comfyui/requirements.txt
       - name: Run Tests
         run: |
           pytest tests/
+        env:
+          PYTHONPATH: ./comfyui
+      - name: Run Linting
+        run: |
+          ruff check .