Canonical CI: grouped-tests.yml + root test/test_groups.toml (#462)

Convert the root Tests.yml test workflow into a thin caller of the
canonical SciML/.github grouped-tests.yml@v1 reusable workflow, with the
group x version matrix declared once in test/test_groups.toml.

The previous workflow hand-maintained a {version: [1, lts, pre]} x
{group: [Core, QA]} matrix calling tests.yml@v1. That matrix now lives in
test/test_groups.toml (Core and QA each on ["1", "lts", "pre"]) and is
computed by compute_affected_sublibraries.jl --root-matrix.

runtests.jl already dispatches on the standard GROUP env var (Core/QA), so
no group-env-name input is needed and no runtests.jl change is required.
No check-bounds/coverage/apt-packages overrides were used by the old job,
so the thin caller carries no `with:` inputs. on: triggers and concurrency
are preserved verbatim; name: "Tests" is kept so branch-protection status
checks remain valid. All other workflow files are untouched.

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/Tests.yml

@@ -16,19 +16,5 @@ concurrency:
 
 jobs:
   tests:
-    name: "Tests"
-    strategy:
-      fail-fast: false
-      matrix:
-        version:
-          - "1"
-          - "lts"
-          - "pre"
-        group:
-          - "Core"
-          - "QA"
-    uses: "SciML/.github/.github/workflows/tests.yml@v1"
-    with:
-      julia-version: "${{ matrix.version }}"
-      group: "${{ matrix.group }}"
+    uses: "SciML/.github/.github/workflows/grouped-tests.yml@v1"
     secrets: "inherit"

test/test_groups.toml

@@ -0,0 +1,5 @@
+[Core]
+versions = ["1", "lts", "pre"]
+
+[QA]
+versions = ["1", "lts", "pre"]