Simplify root CI to grouped-tests.yml (matrix from test/test_groups.toml)

[ChrisRackauckas-Claude]

What

Replaces the hand-maintained group × version matrix in the root .github/workflows/CI.yml test job with the thin grouped-tests.yml@v1 caller. The matrix now lives in the root test/test_groups.toml and is computed by compute_affected_sublibraries.jl --root-matrix.

jobs:
  tests:
    uses: "SciML/.github/.github/workflows/grouped-tests.yml@v1"
    with:
      coverage-directories: "src,lib/OptimizationBase/src,..."
    secrets: "inherit"

• name: CI and the filename are unchanged, so the branch-protection status-check name is preserved.
• on: triggers and concurrency: are kept verbatim.
• coverage-directories is preserved as the only non-default with: input.
• Group dispatch stays on the default GROUP env var, which the root test/runtests.jl reads (get(ENV, "GROUP", "Core")). coverage (true) and check-bounds (yes) keep their defaults, matching the old root tests.yml@v1 call.
• The SublibraryCI.yml workflow (which calls sublibrary-project-tests.yml@v1) and the IntegrationTest/Downstream.yml workflow are untouched.

test/test_groups.toml

Trimmed to exactly the groups the root CI workflow actually ran:

[Core]
versions = ["lts", "1", "pre"]

[QA]
versions = ["lts", "1"]

The GPU group that the monorepo uniformization (#1220) added to this file speculatively is dropped: the root CI.yml never dispatched a GPU job (there was no self-hosted GPU runner cell), so keeping it would invent a matrix entry that did not run before and would attempt to schedule on a self-hosted GPU runner.

Verified matrix match (5/5 exact)

julia compute_affected_sublibraries.jl <repo> --root-matrix yields exactly the old workflow's set:

group	versions
Core	lts, 1, pre
QA	lts, 1

{(Core,lts),(Core,1),(Core,pre),(QA,lts),(QA,1)} — no missing, no extra. TOML and YAML both parse cleanly. Package test suite not run locally (heavy; CI validates).

Ignore until reviewed by @ChrisRackauckas.

🤖 Generated with Claude Code