test(@angular-devkit/build-angular): increase rebuild debounce times

CI performance variability can cause test flakes in rebuild tests due to the rebuilds taking longer than expected.  This change increases the 500ms debounce time for the web worker rebuild tests to 1000ms to mitigate these issues.

(cherry picked from commit c75a48d)

Author: clydin

packages/angular_devkit/build_angular/src/browser/specs/web-worker_spec.ts

@@ -147,7 +147,7 @@ describe('Browser Builder Web Worker support', () => {
     const { run } = await timer(1000).pipe(
       switchMap(() => architect.scheduleTarget(target, overrides)),
       switchMap(run => run.output.pipe(map(output => ({ run, output })))),
-      debounceTime(500),
+      debounceTime(1000),
       tap(({ output }) => expect(output.success).toBe(true, 'build should succeed')),
       tap(() => {
         switch (phase) {