Reject invalid boolean input values - #1159

Description:
Invalid non-empty boolean inputs were silently treated as false, which could disable requested behavior without any signal. This change makes boolean input parsing strict across all affected inputs and fails early with the input name and invalid value.

• Parsing behavior

  • Accept only true and false for:
    • check-latest
    • force-download
    • set-default
    • verify-signature
    • overwrite-settings
    • show-download-progress
    • problem-matcher
  • Preserve case-insensitive parsing.
  • Trim surrounding whitespace before validation.
  • Continue using the configured default when the input is empty.

• Validation failure

  • Invalid non-empty values now throw a descriptive error instead of being coerced to false.

• Test coverage

  • Add unit coverage for valid values, defaults, casing, whitespace, and invalid values for all affected inputs.

Example invalid input now fails fast:

- uses: actions/setup-java@v6
  with:
    distribution: temurin
    java-version: '21'
    verify-signature: ture

Related issue:
Handled automatically by the system.

Check list:

• Ran npm run check locally (format, lint, build, test) and all checks pass.
• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

• Fixes Reject invalid values for boolean inputs #1157