[PHP] Use @throws (#32565)

https://docs.phpdoc.org/3.0/guide/references/phpdoc/tags/throws.html#throws

src/php/lib/Grpc/BaseStub.php

@@ -145,7 +145,7 @@ class BaseStub
      * @param int $timeout in microseconds
      *
      * @return bool true if channel is ready
-     * @throw Exception if channel is in FATAL_ERROR state
+     * @throws Exception if channel is in FATAL_ERROR state
      */
     public function waitForReady($timeout)
     {
@@ -183,7 +183,7 @@ class BaseStub
      * @param $new_state Connect state
      *
      * @return bool true if state is CHANNEL_READY
-     * @throw Exception if state is CHANNEL_FATAL_FAILURE
+     * @throws Exception if state is CHANNEL_FATAL_FAILURE
      */
     private function _checkConnectivityState($new_state)
     {
@@ -242,7 +242,7 @@ class BaseStub
      * @param array $metadata The metadata map
      *
      * @return array $metadata Validated and key-normalized metadata map
-     * @throw InvalidArgumentException if key contains invalid characters
+     * @throws InvalidArgumentException if key contains invalid characters
      */
     private function _validate_and_normalize_metadata($metadata)
     {