Fix YAML validation errors in self-hosted-runner.yml workflow

[Copilot]

The self-hosted-runner.yml workflow was failing yamllint validation due to formatting issues that prevented proper GitHub Actions processing.

Changes

YAML formatting compliance:

• Added document start marker (---)
• Fixed bracket spacing: branches: [ main ] → branches: [main]
• Quoted truthy value: on: → "on":"
• Removed trailing whitespace on lines 60, 110

Line length compliance (80 char limit):

# Before: 109 characters
echo "- **OS**: $(cat /etc/os-release | grep PRETTY_NAME | cut -d= -f2 | tr -d '\"')" >> $GITHUB_STEP_SUMMARY

# After: Split with intermediate variables
OS_REL="/etc/os-release"
OS_NAME=$(cat $OS_REL | grep PRETTY_NAME | cut -d= -f2 | tr -d '\"')
echo "- **OS**: $OS_NAME" >> $GITHUB_STEP_SUMMARY

Long conditionals:

# Before: 118 characters
if: ${{ contains(github.event.head_commit.message, '[test-runner]') || github.event_name == 'workflow_dispatch' }}

# After: Block scalar notation
if: >-
  ${{ contains(github.event.head_commit.message, '[test-runner]')
  || github.event_name == 'workflow_dispatch' }}

Applied similar fixes to memory, disk, and result variable assignments. No functional changes to workflow execution.

Original prompt

Fix Self-Hosted Runner Validation workflow failure (issue #734)

The self-hosted-runner.yml workflow is failing validation. Please analyze the workflow, identify issues, and implement fixes.

References:

• Issue: Fix: Self-Hosted Runner Validation workflow failure (Run 19146999120) #734
• Workflow: .github/workflows/self-hosted-runner.yml

Please ensure runner validation passes after your fix.

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