`@angular/build:unit-test` with Vitest test runner throws `Failed to import test file` error

### Command

test

### Is this a regression?

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

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

_No response_

### Description

Steps to reproduce:

1. Create a `TestService` that will contain a single property `router = inject(Router)`
2. Configure `@angular/build:unit-test` runner to include `providersFile`
3. Export `[TestService]` from it
4. Create a `Test` component that will inject this service: `service = inject(TestService)`

`ng test` will fail with the following error **for all specs**:

```
FAIL project (chromium) path/to/some.spec.ts [ path/to/some.spec.ts ]
Error: Failed to import test file /project/root/init-testbed.js
Caused by: Error: The injectable '_PlatformLocation' needs to be compiled using the JIT compiler, but '@angular/compiler' is not available.

The injectable is part of a library that has been partially compiled.
However, the Angular Linker has not processed the library such that JIT compilation is used as fallback.

Ideally, the library is processed using the Angular Linker to become fully AOT compiled.
Alternatively, the JIT compiler should be loaded by bootstrapping using '@angular/platform-browser-dynamic' or '@angular/platform-server',
or manually provide the compiler with 'import "@angular/compiler";' before bootstrapping.
❯ node_modules/.vite/vitest/dc540563f7f56f2cac74b38788615874d1da1c10/deps/chunk-42LDSDVL.js?v=049c4943:83:17
```

If you remove injection of the `TestService` from the `Test` component **all the specs** will start to pass.

### Minimal Reproduction

https://github.com/th0r/ng-vitest-test-providers-bug

### Your Environment

```
Angular CLI : 21.0.1
Angular : 21.0.2
Node.js : 24.8.0
Package Manager : npm 11.6.0
Operating System : darwin arm64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build │ 21.0.1 │ ^21.0.1 │
│ @angular/cli │ 21.0.1 │ ^21.0.1 │
│ @angular/common │ 21.0.2 │ ^21.0.0 │
│ @angular/compiler │ 21.0.2 │ ^21.0.0 │
│ @angular/compiler-cli │ 21.0.2 │ ^21.0.0 │
│ @angular/core │ 21.0.2 │ ^21.0.0 │
│ @angular/forms │ 21.0.2 │ ^21.0.0 │
│ @angular/platform-browser │ 21.0.2 │ ^21.0.0 │
│ @angular/router │ 21.0.2 │ ^21.0.0 │
│ rxjs │ 7.8.2 │ ~7.8.0 │
│ typescript │ 5.9.3 │ ~5.9.2 │
│ vitest │ 4.0.14 │ ^4.0.8 │
└───────────────────────────┴───────────────────┴───────────────────┘
```

Comienza revisando el manejo de providersFile del runner @angular/build:unit-test y el init-testbed.js generado; después reproduce el fallo usando el repositorio mínimo enlazado. Verifica la corrección ejecutando ng test con TestService inyectando Router y confirmando que todas las specs se importan y pasan sin el error del compilador JIT.

Escrito por el modelo de indexación a partir del texto del issue.