[BUG] not installing peer dependencies for workspaces if they are not nested inside the root package

Current Behavior:

having 'library-project' with peer-dependencies adjacent to 'main-project'
and 'main-project' with workspaces: ['../library-project'] (outside of 'main-project' folder)
'npm install' in 'main-project' is not installing the peer-dependencies

example:

library-project/
  package.json      // peerDependencies: {"dep-a": "1.0.0"}
main-project/
  package.json      // "workspaces": [ "../library-project" ]

Expected Behavior:

expecting node_modules in 'main-project' after 'npm i' to include 'dep-a':

node_modules
  library-project (linked)
  dep-a

actual result: missing 'dep-a' in node_modules

this works fine if 'library-project' would be inside 'main-project'

Steps To Reproduce:

1. main-project and library-project are two adjacent projects

2. main-project package.json:

{
  "name": "main-project",
  "version": "1.0.0",
  "workspaces": [
    "../library-project"
  ],
  "dependencies": {
    "library-project": "1.0.0"
  }
}

3. library-project package.json:

{
  "name": "library-project",
  "version": "1.0.0",
  "peerDependencies": {
    "@angular/core": "11.1.2"
  }
}

4. run 'npm install' in 'main-project'

5. expected "@angular/core" to be installed as it's a peer dependency of 'library-project'

Environment:

• Node: 15.6.0
• npm: 7.5.2

Reproduce the issue with adjacent main-project and library-project directories using the package.json files and npm 7.5.2 described here. Start by tracing workspace linking and peer-dependency installation for a workspace outside the root; done when running npm install in main-project installs the library project's peer dependency, such as @angular/core, in main-project/node_modules.