Canonical CI: grouped-tests.yml + root test/test_groups.toml (#382)

Convert the root CI workflow (ci.yml) to the canonical thin caller of
SciML/.github grouped-tests.yml@v1, with the group x version matrix
declared once in test/test_groups.toml instead of hand-maintained YAML.

The previously inlined matrix (group: Core/Autodiff/GPU/Downstream/
Reactant/nopre x version: lts/1/pre, with pre excluded for nopre/
Downstream/Reactant) is reproduced exactly by test_groups.toml:
15/15 (group, version) cells match the compute_affected_sublibraries.jl
--root-matrix output. runtests.jl already dispatches on the standard
GROUP env var, so no with: overrides and no runtests.jl change needed.

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/ci.yml

@@ -11,31 +11,6 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
 jobs:
-  test:
-    name: Tests
-    strategy:
-      fail-fast: false
-      matrix:
-        group:
-          - Core
-          - Autodiff
-          - GPU
-          - Downstream
-          - Reactant
-          - nopre
-        version:
-          - 'lts'
-          - '1'
-          - 'pre'
-        exclude:
-          - group: nopre
-            version: 'pre'
-          - group: Downstream
-            version: 'pre'
-          - group: Reactant
-            version: 'pre'
-    uses: "SciML/.github/.github/workflows/tests.yml@v1"
-    with:
-      group: "${{ matrix.group }}"
-      julia-version: "${{ matrix.version }}"
+  tests:
+    uses: "SciML/.github/.github/workflows/grouped-tests.yml@v1"
     secrets: "inherit"

test/test_groups.toml

@@ -0,0 +1,17 @@
+[Core]
+versions = ["lts", "1", "pre"]
+
+[Autodiff]
+versions = ["lts", "1", "pre"]
+
+[GPU]
+versions = ["lts", "1", "pre"]
+
+[Downstream]
+versions = ["lts", "1"]
+
+[Reactant]
+versions = ["lts", "1"]
+
+[nopre]
+versions = ["lts", "1"]