fix(@angular/build): use an empty array as default value for vitest exclude

Fixes #30543

Avoids the error `resolved.coverage.exclude is not iterable` while running `ng test`.

Author: cexbrayat

packages/angular/build/src/builders/unit-test/builder.ts

@@ -233,7 +233,7 @@ export async function* execute(
           coverage: {
             enabled: !!normalizedOptions.codeCoverage,
             excludeAfterRemap: true,
-            exclude: normalizedOptions.codeCoverage?.exclude,
+            exclude: normalizedOptions.codeCoverage?.exclude ?? [],
             // Special handling for `reporter` due to an undefined value causing upstream failures
             ...(normalizedOptions.codeCoverage?.reporters
               ? { reporters: normalizedOptions.codeCoverage.reporters }