v21.2.2 seems to be unable to handle npm workspaces

### Command

update

### Is this a regression?

- [x] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

v20

### Description

While using npm workspaces, `ng update @angular/core@21` (or any other angular package) with installed version `@angular/cli@21` fails with the following error:
```
Using package manager: npm
Collecting installed dependencies...
Found 1 dependencies.
Package '@angular/core' is not a dependency.
```
This does not happen in the same repo with v20 installed (and trying to update to v20). It also does not happen in a repo without npm workspaces.

### Minimal Reproduction

See https://github.com/jsangmeister/angular-cli-repro

I created the repo as follows:
```
npm init
mkdir apps
cd apps
ng new test-app
```
and then moving some files to the top level, e.g., the git folder.

When running `cd apps/test-app && ng update @angular/core@21`, the error appears.

### Exception or Error

```text
Package '@angular/core' is not a dependency.
```

### Your Environment

```text
_ _ ____ _ ___
/ \ _ __ __ _ _ _| | __ _ _ __ / ___| | |_ _|
/ △ \ | '_ \ / _` | | | | |/ _` | '__| | | | | | |
/ ___ \| | | | (_| | |_| | | (_| | | | |___| |___ | |
/_/ \_\_| |_|\__, |\__,_|_|\__,_|_| \____|_____|___|
|___/

Angular CLI : 21.2.2
Angular : 21.2.4
Node.js : 24.10.0
Package Manager : npm 11.9.0
Operating System : linux x64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build │ 21.2.2 │ ^21.2.2 │
│ @angular/cli │ 21.2.2 │ ^21.2.2 │
│ @angular/common │ 21.2.4 │ ^21.2.0 │
│ @angular/compiler │ 21.2.4 │ ^21.2.0 │
│ @angular/compiler-cli │ 21.2.4 │ ^21.2.0 │
│ @angular/core │ 21.2.4 │ ^21.2.0 │
│ @angular/forms │ 21.2.4 │ ^21.2.0 │
│ @angular/platform-browser │ 21.2.4 │ ^21.2.0 │
│ @angular/router │ 21.2.4 │ ^21.2.0 │
│ rxjs │ 7.8.2 │ ~7.8.0 │
│ typescript │ 5.9.3 │ ~5.9.2 │
│ vitest │ 4.1.0 │ ^4.0.8 │
└───────────────────────────┴───────────────────┴───────────────────┘
```

### Anything else relevant?

_No response_

Beginnen Sie mit der verknüpften minimalen Reproduktion und führen Sie `cd apps/test-app 6ff ng update @angular/core@21` mit Angular CLI 21.2.2 in einem npm-workspaces-Repository aus. Vergleichen Sie das Ergebnis mit demselben Update unter v20 oder ohne workspaces; abgeschlossen ist es, wenn Angular-Pakete als Abhängigkeiten erkannt werden und das Update ohne den gemeldeten Fehler fortgesetzt wird.

Vom Indexierungsmodell aus dem Issue-Text verfasst.