doc(test_runner): shards not supported with watch mode

doc/api/test.md

@@ -1135,7 +1135,7 @@ changes:
     If unspecified, subtests inherit this value from their parent.
     **Default:** `Infinity`.
   * `watch` {boolean} Whether to run in watch mode or not. **Default:** `false`.
-  * `shard` {Object} Running tests in a specific shard. **Default:** `undefined`.
+  * `shard` {Object} Running tests in a specific shard. It's not supported with watch mode. **Default:** `undefined`.
     * `index` {number} is a positive integer between 1 and `<total>`
       that specifies the index of the shard to run. This option is _required_.
     * `total` {number} is a positive integer that specifies the total number