`Unrecognized named-value: 'matrix'` / `Available expression contexts: github, inputs, vars, needs, strategy, matrix, secrets, steps, job, runner, env`

Type: Bug

Create a `.github/workflows/ci.yml` file with:
```yaml
name: CI
on:
push:
workflow_dispatch:

env:
REGISTRY: ghcr.io
IMAGE_NAME: ${{ github.repository }}

jobs:
build-arch:
name: Build
permissions:
contents: read
packages: write
attestations: write
id-token: write

strategy:
fail-fast: false
matrix:
include:
- os: ubuntu-24.04
name: amd
- os: ubuntu-24.04-arm
name: arm

runs-on: ${{ matrix.os }}
outputs:
attestation-url: ${{ steps.attestation.outputs.attestation-url }}
${{ matrix.name }}-attestation-url: ${{ steps.attestation.outputs.attestation-url }}
my-matrix: ${{ matrix }}
${{ toJSON(matrix) }}: 'x'

steps:
- name: Checkout
uses: actions/checkout@v4

- name: Log in to the Container registry
uses: docker/login-action@v3
with:
registry: ${{ env.REGISTRY }}
username: ${{ github.actor }}
password: ${{ secrets.GITHUB_TOKEN }}

- name: Extract metadata (tags, labels) for Docker
id: meta
uses: docker/metadata-action@v5
with:
images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}

- name: Build and push Docker image
id: push
uses: docker/build-push-action@v6
with:
context: .
push: true
tags: ${{ steps.meta.outputs.tags }}
labels: ${{ steps.meta.outputs.labels }}

- name: Generate artifact attestation
id: attestation
uses: actions/attest-build-provenance@v2
with:
subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
subject-digest: ${{ steps.push.outputs.digest }}
push-to-registry: true

combine-images:
name: Combine images
permissions:
contents: read
packages: write
attestations: write
id-token: write

runs-on: ubuntu-latest
steps:
- name: Checkout
uses: actions/checkout@v4

- name: Log in to the Container registry
uses: docker/login-action@v3
with:
registry: ${{ env.REGISTRY }}
username: ${{ github.actor }}
password: ${{ secrets.GITHUB_TOKEN }}
```

See a red-squiggly near `${{ matrix.name }}-attestation-url: ${{ steps.attestation.outputs.attestation-url }}`

Hover over `${{ matrix.name }}`

See:
```yaml
Unrecognized named-value: 'matrix'
Available expression contexts: github, inputs, vars, needs, strategy, matrix, secrets, steps, job, runner, env
```

View problem shows:
```yaml
Unrecognized named-value: 'matrix'
```

---

* If an expression is available, then it should be usable.
* If it isn't available, then it shouldn't be listed as available.

Extension version: 0.27.1
VS Code version: Code 1.98.0 (Universal) (6609ac3d66f4eade5cf376d1cb76f13985724bcb, 2025-03-04T21:06:18.612Z)
OS version: Darwin arm64 24.3.0
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|Apple M1 Max (10 x 2400)|
|GPU Status|2d_canvas: enabled
canvas_oop_rasterization: enabled_on
direct_rendering_display_compositor: disabled_off_ok
gpu_compositing: enabled
multiple_raster_threads: enabled_on
opengl: enabled_on
rasterization: enabled
raw_draw: disabled_off_ok
skia_graphite: disabled_off
video_decode: enabled
video_encode: enabled
webgl: enabled
webgl2: enabled
webgpu: enabled
webnn: disabled_off|
|Load (avg)|7, 9, 10|
|Memory (System)|64.00GB (0.87GB free)|
|Process Argv|--crash-reporter-id 1fc67ee2-0174-4598-9f98-4537df0dd32c|
|Screen Reader|no|
|VM|0%|

A/B Experiments

```
vsliv368:30146709
vspor879:30202332
vspor708:30202333
vspor363:30204092
vswsl492:30256859
vscod805cf:30301675
binariesv615:30325510
py29gd2263:31024239
c4g48928:30535728
azure-dev_surveyone:30548225
vscrp:30673768
962ge761:30959799
h48ei257:31000450
pythontbext0:30879054
cppperfnew:31000557
dwnewjupytercf:31046870
nativerepl2:31139839
pythonrstrctxt:31112756
nativeloc2:31192216
iacca1:31171482
5fd0e150:31155592
dwcopilot:31170013
6074i472:31201624
dwoutputs:31242946
customenabled:31248079
5a9hg449:31230677
hdaa2157:31222309
copilot_t_ci:31222730
jda6j935:31233686

```

Tái hiện chẩn đoán trong ví dụ `.github/workflows/ci.yml` bằng VS Code 1.98.0 và GitHub Actions extension 0.27.1. Bắt đầu bằng cách lần theo quá trình xác thực các output ở cấp job có tham chiếu đến `matrix`; hoàn tất khi chẩn đoán phản ánh chính xác việc context đó có thể sử dụng được hay không và không còn mâu thuẫn với các context khả dụng được liệt kê.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.