test: update css minification spec to match new Esbuild output

For more context see https://github.com/evanw/esbuild/blob/master/CHANGELOG.md#%E2%80%8B0137

(cherry picked from commit ba54a8d)

Author: alan-agius4

packages/angular_devkit/build_angular/src/builders/browser/specs/styles_spec.ts

@@ -653,6 +653,6 @@ describe('Browser Builder styles', () => {
     });
 
     result = await browserBuild(architect, host, target, { optimization: true });
-    expect(await result.files['styles.css']).toContain('rgba(0,0,0,.149)');
+    expect(await result.files['styles.css']).toContain('rgba(0,0,0,.15)');
   });
 });