docs: mention Vitest instead of Karma in README template of schematic…

[guisalmeida]

PR Checklist

Please check to confirm your PR fulfils the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Since version Angular 21, Vitest is the default test runner.

Issue Number: N/A

What is the new behavior?

Mention Vitest instead of Karma.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Found a similar change in #31916, but it seems this part in the schematic/library files was forgotten to change as well.

[gemini-code-assist]

Code Review

This pull request updates the library README template to reference the Vitest test runner instead of Karma. The review feedback correctly points out that since Karma is still supported as a fallback, hardcoding Vitest will lead to incorrect documentation. It is recommended to dynamically display the test runner name based on the template context.

[gemini-code-assist]

Since the library schematic still supports Karma as a test runner (as seen in packages/schematics/angular/library/index.ts where it falls back to the Karma builder if Vitest is not selected), hardcoding Vitest in the README template will result in incorrect documentation when a user generates a library with Karma.

We can dynamically display the correct test runner in the README by checking the testTypesPackage template variable, which is already passed to the template context.

To execute unit tests with the <%= testTypesPackage === 'vitest/globals' ? '[Vitest](https://vitest.dev/)' : '[Karma](https://karma-runner.github.io)' %> test runner, use the following command: