Lack of both steps and uses isn't flagged as an error

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
Steps to reproduce the behavior:
1. With this workflow `csharp-qltest.yml`:
```yml
name: "C#: Run QL Tests"

on:
push:
paths:
- "csharp/**"
- "shared/**"
- .github/actions/fetch-codeql/action.yml
- codeql-workspace.yml
branches:
- main
- "rc/*"
pull_request:
paths:
- "csharp/**"
- "shared/**"
- .github/workflows/csharp-qltest.yml
- .github/actions/fetch-codeql/action.yml
- codeql-workspace.yml
branches:
- main
- "rc/*"

defaults:
run:
working-directory: csharp

jobs:
qlupgrade:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- uses: ./.github/actions/fetch-codeql
- name: Check DB upgrade scripts
run: |
echo >empty.trap
codeql dataset import -S ql/lib/upgrades/initial/semmlecode.csharp.dbscheme testdb empty.trap
codeql dataset upgrade testdb --additional-packs ql/lib
diff -q testdb/semmlecode.csharp.dbscheme ql/lib/semmlecode.csharp.dbscheme
- name: Check DB downgrade scripts
run: |
echo >empty.trap
rm -rf testdb; codeql dataset import -S ql/lib/semmlecode.csharp.dbscheme testdb empty.trap
codeql resolve upgrades --format=lines --allow-downgrades --additional-packs downgrades \
--dbscheme=ql/lib/semmlecode.csharp.dbscheme --target-dbscheme=downgrades/initial/semmlecode.csharp.dbscheme |
xargs codeql execute upgrades testdb
diff -q testdb/semmlecode.csharp.dbscheme downgrades/initial/semmlecode.csharp.dbscheme

choose-runner:
runs-on: ubuntu-latest
outputs:
mac-12: ${{ vars.use-large-mac-runners-for-speed && 'mac-12-xl' || 'mac-12' }}
ubuntu-latest: ${{ vars.use-large-linux-runners-for-speed && 'ubuntu-latest-xl' || 'ubuntu-latest' }}
windows-latest: ${{ vars.use-large-win-runners-for-speed && 'windows-latest-xl' || 'windows-latest' }}

qltest:
needs: choose-runner
runs-on: ${{ needs.choose-runner.outputs.ubuntu-latest }}
strategy:
fail-fast: false
matrix:
slice: ["1/2", "2/2"]
steps:
- uses: actions/checkout@v4
- uses: ./csharp/actions/create-extractor-pack
- name: Cache compilation cache
id: query-cache
uses: ./.github/actions/cache-query-compilation
with:
key: csharp-qltest-${{ matrix.slice }}
- name: Run QL tests
run: |
codeql test run --threads=0 --ram 50000 --slice ${{ matrix.slice }} --search-path extractor-pack --check-databases --check-undefined-labels --check-repeated-labels --check-redefined-labels --consistency-queries ql/consistency-queries ql/test --compilation-cache "${{ steps.query-cache.outputs.cache-dir }}"
env:
GITHUB_TOKEN: ${{ github.token }}
unit-tests:
strategy:
matrix:
os: [ubuntu-latest, windows-2019]
runs-on: ${{ matrix.os }}
steps:
- uses: actions/checkout@v4
- name: Setup dotnet
uses: actions/setup-dotnet@v4
with:
dotnet-version: 8.0.100
- name: Extractor unit tests
run: |
dotnet test -p:RuntimeFrameworkVersion=8.0.0 extractor/Semmle.Util.Tests
dotnet test -p:RuntimeFrameworkVersion=8.0.0 extractor/Semmle.Extraction.Tests
dotnet test -p:RuntimeFrameworkVersion=8.0.0 autobuilder/Semmle.Autobuild.CSharp.Tests
dotnet test -p:RuntimeFrameworkVersion=8.0.0 "${{ github.workspace }}/cpp/autobuilder/Semmle.Autobuild.Cpp.Tests"
shell: bash
stubgentest:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v4
- uses: ./csharp/actions/create-extractor-pack
- name: Run stub generator tests
run: |
# Generate (Asp)NetCore stubs
STUBS_PATH=stubs_output
python3 scripts/stubs/make_stubs_nuget.py webapp Swashbuckle.AspNetCore.Swagger 6.5.0 "$STUBS_PATH"
rm -rf ql/test/resources/stubs/_frameworks
# Update existing stubs in the repo with the freshly generated ones
mv "$STUBS_PATH/output/stubs/_frameworks" ql/test/resources/stubs/
git status
codeql test run --threads=0 --search-path extractor-pack --check-databases --check-undefined-labels --check-repeated-labels --check-redefined-labels --consistency-queries ql/consistency-queries -- ql/test/library-tests/dataflow/flowsources/aspremote
env:
GITHUB_TOKEN: ${{ github.token }}
```

2. Look at the choose-runner job

**Expected behavior**

According to GitHub, this job isn't valid:
https://github.com/jsoref/codeql/actions/runs/7712430252
> [Invalid workflow file: .github/workflows/csharp-qltest.yml#L1](https://github.com/jsoref/codeql/actions/runs/7712430252/workflow)
No steps defined in `steps` and no workflow called in `uses` for the following jobs: choose-runner

Generally if a workflow isn't valid, this extension will complain, e.g. if I add just `steps:`:

**Screenshots**
[Invalid workflow file: .github/workflows/csharp-qltest.yml#L1](https://github.com/jsoref/codeql/actions/runs/7712430252/workflow)
No steps defined in `steps` and no workflow called in `uses` for the following jobs: choose-runner

**Extension Version**
`v0.26.2`

**Additional context**

Reproduce the validation issue with .github/workflows/csharp-qltest.yml and the referenced GitHub Actions run, focusing on the choose-runner job that has outputs but neither steps nor uses. Trace the workflow validation entry point and existing tests for invalid job definitions. Done means the extension reports this invalid workflow while preserving the existing diagnostic for a job with only steps.

由索引模型根据 Issue 内容生成。