QA: restore Aqua deps_compat (add missing [compat] for test extras)

[ChrisRackauckas-Claude]

Problem

The grouped-tests CI conversion added Pkg to [extras]/[targets].test in the package Project.toml without a corresponding [compat] entry. This trips Aqua's test_deps_compat extras sub-check.

The conversion worked around this by weakening the check rather than fixing the metadata: Aqua.test_deps_compat(EllipsisNotation, check_extras = false) plus a @test_broken false sentinel, with a tracking issue (#113).

Fix (metadata only, one-line)

1. Add the missing Pkg = "1" to [compat] in the root Project.toml.
2. Restore the full Aqua.test_deps_compat(EllipsisNotation) call in test/qa.jl and remove the check_extras = false weakening + @test_broken false sentinel.

This is CI-hygiene (metadata + re-enabling a check), not a test-logic change.

Local verification

GROUP=QA julia +1.11 ... Pkg.test() passes:

Quality Assurance |   10     10  27.3s
Explicit Imports  |    2      2
JET               |   14     14
Testing EllipsisNotation tests passed

Closes #113 (that issue covered only this deps_compat nit).

Ignore until reviewed by @ChrisRackauckas.

[ChrisRackauckas-Claude]

Note: this PR was opened with --draft but the account lacks permission to set/keep the draft flag on this repo, so it shows as ready. It is not ready for merge — please treat it as a draft. Ignore until reviewed by @ChrisRackauckas.