fix: preserve root path in tryWorkspaceByCwd when cwd is /

[quinise]

What's the problem this PR addresses?

In Project.tryWorkspaceByCwd, the workspaceCwd is normalized and trailing slashes are stripped. However, when cwd is the filesystem root (/), stripping the trailing slash produces an empty string "" instead of "/", causing workspace lookup to fail.

Closes issue #5380
[Bug?]: The nearest package directory (/) doesn't seem to be part of the project declared in /. (docker)

...

How did you fix it?

After stripping trailing slashes, fall back to PortablePath.root if the result is an empty string:

// Before
workspaceCwd = ppath.normalize(workspaceCwd).replace(/\/+$/, ``) as PortablePath;

// After
workspaceCwd = (ppath.normalize(workspaceCwd).replace(/\/+$/, ``) || PortablePath.root) as PortablePath;

...

Checklist

• I have read the Contributing Guide.

• I have set the packages that need to be released for my changes to be effective.

• [] I will check that all automated PR checks pass before the PR gets reviewed.

[Copilot]

Pull request overview

Fixes a workspace lookup edge case in Project.tryWorkspaceByCwd where normalizing / and stripping trailing slashes could produce an empty string, causing workspace resolution to fail when the current working directory is the filesystem root (notably in Docker scenarios).

Changes:

• Preserve the filesystem root by falling back to PortablePath.root when trailing-slash stripping would yield ''.
• Add a regression test ensuring tryWorkspaceByCwd('/') can resolve a workspace registered at /.
• Add a versions file to release the fix as patch updates across relevant Yarn packages/plugins.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/yarnpkg-core/sources/Project.ts	Ensures normalized root path (/) isn’t converted into an empty string during workspace lookup.
packages/yarnpkg-core/tests/Project.test.ts	Adds a regression test covering workspace lookup when cwd is /.
.yarn/versions/da7e1fc4.yml	Declares patch releases for packages affected by the core fix.

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