CI: Fix workflow matrix exclusion logic with empty strings

[justin808]

Problem

The exclude logic in our GitHub Actions workflows has a potential issue where conditional expressions can produce empty strings that won't match any matrix values:

exclude:
  - ruby-version: ${{ github.event_name == 'pull_request' && github.ref \!= 'refs/heads/master' && '3.2' || '' }}
    node-version: ${{ github.event_name == 'pull_request' && github.ref \!= 'refs/heads/master' && '20' || '' }}
    dependency-level: ${{ github.event_name == 'pull_request' && github.ref \!= 'refs/heads/master' && 'minimum' || '' }}

When the condition is false (e.g., on master branch), this produces empty strings ('') which won't match any actual matrix values. This makes the exclusion ineffective in those cases.

Impact

Currently, this works as intended on PRs (excludes minimum dependency tests). However, the logic is fragile and could cause issues if:

• Matrix values change
• Someone expects exclusions to work differently
• We add more conditional exclusions

Affected Files

• .github/workflows/main.yml: Lines 55-58, 146-149
• .github/workflows/examples.yml: Lines 54-56

Proposed Solutions

Option 1: Use separate jobs with conditions

jobs:
  test-latest:
    # Always runs
    
  test-minimum:
    if: github.ref == 'refs/heads/master' || github.event_name == 'workflow_dispatch'

Option 2: Use conditional includes instead of excludes

include:
  - ruby-version: '3.4'
    node-version: '22'
    dependency-level: 'latest'
  - ${{ github.ref == 'refs/heads/master' && { ruby-version: '3.2', node-version: '20', dependency-level: 'minimum' } || {} }}

Option 3: Use reusable workflows

Create separate workflow files for latest vs minimum dependency testing.

Priority

Medium - The current implementation works but is fragile and could break with future changes.

Related

Part of the CI reliability improvements from PR #1995.