fix: correct main entry for relative path

[milaninfy]

npm-packlist gets normalized package-json when assessing files to include. when main is specified with relative file path it doesn't consider that entry when including files. Fixing main in normalization step

• [x] check on changes condition
• [x] sanity testing
• [x] check npm pack command with empty files array in package.json
  • [ ] arborist node uses read-package-json-fast normalization functionality instead of package-json's normalization flow
• [ ] need to check for read-package-json-fast's normalization logic to replace it with package-json's normalization

Fixes: https://github.com/npm/cli/issues/7799