fix(ci): drop the 1x1 matrix so the required check name is actually stable

[hyperpolymath]

Closes #38.

What #39 got wrong

#39 renamed the job to Julia tests and I reported the required check as version-stable. It is not, and I never measured the thing that matters. Measured on #39's own head 776e340d, after it had landed:

what GitHub actually posted	Julia tests (1.12.5, ubuntu-24.04)
what the ruleset requires	Julia tests

GitHub appends the matrix combination to a job's posted check name whenever the name: does not itself reference the matrix. The old name, Julia ${{ matrix.julia-version }} / ${{ matrix.os }}, suppressed the suffix by accident; replacing it with a static string switched the suffix on. A 1×1 matrix is still a matrix.

So both pins stayed embedded in the check name, the required context Julia tests was never reported at all, and main has been sitting in exactly the deadlock this issue describes — #39 merged only because an admin bypass was available. The bump demonstration in that PR parsed the YAML name: field and called it "the check name"; it could not have caught this.

The control was in the same output all along: Repo hygiene (licence · format · lint · commit), a job with no matrix, posts its name: verbatim.

The fix

The matrix selected exactly one combination and bought nothing, so it is removed rather than worked around:

• runs-on: ubuntu-24.04 — a literal, because runs-on cannot read env
• setup-julia version: "1.12.5" — a literal

Each keeps the reasoning that used to sit beside its matrix entry. The ruleset context is unchanged — Julia tests was always the target state; the only thing wrong was what the workflow posted.

Why the guard did not catch it

test_install_pins.jl asserted that no job name interpolates anything — a property of the YAML name: field — while the consumer, the ruleset, matches the rendered check-run name. The guard asked a different question than its consumer, so it passed on a broken fix.

It now asserts both necessary conditions, over every job in the file:

1. the name interpolates nothing, and
2. the job has no strategy.matrix.

Run against the previous commit, that assertion fails on test alone — 5 pass / 1 fail — so it discriminates rather than blanket-failing. If a matrix is ever genuinely wanted, the required context must first move to a matrix-free aggregator job, and the comment says so.

CI installs what is pinned made the same claims about the same two values and is repointed at where they now live, locating the setup step by its uses: rather than by index. Mutating either literal fails it (verified: version → 1.12.6, runs-on → ubuntu-latest, one failure each at the right line).

Acceptance criteria

#	criterion	status
1	version-stable job name	the posted check name must read exactly Julia tests — evidence added as a comment below, read off this PR's head, not off the YAML
2	ruleset context updated in the same change	already Julia tests; unchanged, and now actually satisfiable
3	bump demonstrated	a pin bump changes only the literal; the posted name cannot move, because there is no matrix to append
4	test_install_pins.jl passing	102 / 102

🤖 Generated with Claude Code

https://claude.ai/code/session_01X3hgXxWm6umMgZkjYyHnnm

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• .github/workflows/ci.yml
• test/unit/test_install_pins.jl

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Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
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0.0% Coverage on New Code
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