Do not add local package to lockfile

[tgolsson]

Replaces #1470

Pull Request Check List

• A news fragment is added in news/ describing what is new.
• Test cases added for changed code.

Describe what you have changed in this PR.

If you have a pyproject where you depend on yourself using the pattern described in #1441, with a config such as this:

[project]
name = "pkg"
version = "0.2.0"
dependencies = []

requires-python = ">=3.8"
license = {text = "MIT"}

[project.optional-dependencies]
foobar = ["pyyaml"]
ci = ["pkg[foobar]"]

The project will appear multiple times in the lockfile. Changing the version or name of the local package will desync from the lockfile; leading to pdm sync failing. This PR removes the local package from the lockfile, and instead adds a generator for it when running from a LockedRepository.

This works and all tests pass. I did however notice that when using this pattern the local package gets installed twice; but that happens on main as well:

$ pdm --version
PDM, version 2.2.0
$ pdm install -G ci
Synchronizing working set with lock file: 2 to add, 0 to update, 0 to remove

  ✔ Install pkg 0.2.0 successful
  ✔ Install pyyaml 6.0 successful
Installing the project as an editable package...
  ✔ Install pkg 0.2.0 successful

🎉 All complete!

Not sure if there's a good opportunity to fix that here as well.

[frostming]

I did however notice that when using this pattern the local package gets installed twice; but that happens on main as well:

It can be fixed by dropping the self-package from the resolution result. Then no need to skip it in format_lockfile anymore.

[frostming]

Wrong import path, please fix it

[frostming]

It seems the latest ubuntu runner has some issues with setup-python 3.6. But I can't find a bug report about this.