ci: reduce bazel test shards for browser builder test

Reduce the number of test shards for the browser builder from 50 to 10.
50 is more than needed and can cause excessive resource usage.

Author: clydin

packages/angular_devkit/build_angular/BUILD.bazel

@@ -352,7 +352,7 @@ LARGE_SPECS = {
     },
     "ng-packagr": {},
     "browser": {
-        "shards": 50,
+        "shards": 10,
         "size": "large",
         "flaky": True,
         "extra_deps": [