Correct for local package installs always being treated as editable.

[matteius]

The issue

Fixes #6221

The fix

Local file installs were not considering if user wanted it marked editable. This was a regression, that seems like it has been long standing at this point.

The checklist

• [X] Associated issue
• [X] A news fragment in the news/ directory to describe this fix with the extension .bugfix.rst, .feature.rst, .behavior.rst, .doc.rst. .vendor.rst. or .trivial.rst (this will appear in the release changelog). Use semantic line breaks and name the file after the issue number or the PR #.