fix(@angular/build): only require karma-coverage when coverage is enabled

The upfront dependency validation of the unit-test builder's karma runner checks
the truthiness of the normalized `coverage` option, which is always an object
since the introduction of the advanced coverage options. As a result, `ng test`
with the karma runner fails with a `MissingDependenciesError` requesting the
`karma-coverage` package even when coverage is disabled. Check the `enabled`
property instead, matching the vitest runner and the karma executor. A new unit
spec for the karma runner's dependency validation fails without this change.

Author: MeAkib

packages/angular/build/src/builders/unit-test/runners/karma/index.ts

@@ -30,7 +30,7 @@ const KarmaTestRunner: TestRunner = {
       }
     }
 
-    if (options.coverage) {
+    if (options.coverage.enabled) {
       checker.check('karma-coverage');
     }
 

packages/angular/build/src/builders/unit-test/runners/karma/index_spec.ts

@@ -0,0 +1,33 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import type { NormalizedUnitTestBuilderOptions } from '../../options';
+import KarmaTestRunner from './index';
+
+describe('KarmaTestRunner', () => {
+  describe('validateDependencies', () => {
+    function createOptions(coverageEnabled: boolean): NormalizedUnitTestBuilderOptions {
+      return {
+        projectSourceRoot: '/non-existent',
+        coverage: { enabled: coverageEnabled },
+      } as NormalizedUnitTestBuilderOptions;
+    }
+
+    it('does not require karma-coverage when coverage is disabled', () => {
+      expect(() => KarmaTestRunner.validateDependencies?.(createOptions(false))).toThrowError(
+        /^(?!.*karma-coverage)/s,
+      );
+    });
+
+    it('requires karma-coverage when coverage is enabled', () => {
+      expect(() => KarmaTestRunner.validateDependencies?.(createOptions(true))).toThrowError(
+        /karma-coverage/,
+      );
+    });
+  });
+});