Added PHP 8.4 Support for Elasticsearch 6.8.x (#1420)

* Fix "Implicitly nullable parameter" deprecation in PHP 8.4

* GitHub Actions: Add PHP 8.4 version to the test matrix

Author: dakujem

src/Elasticsearch/ClientBuilder.php

@@ -394,7 +394,7 @@ public function setSniffOnStart(bool $sniffOnStart): ClientBuilder
      * @param null|string $password
      * @return $this
      */
-    public function setSSLCert(string $cert, string $password = null): ClientBuilder
+    public function setSSLCert(string $cert, ?string $password = null): ClientBuilder
     {
         $this->sslCert = [$cert, $password];
 
@@ -406,7 +406,7 @@ public function setSSLCert(string $cert, string $password = null): ClientBuilder
      * @param null|string $password
      * @return $this
      */
-    public function setSSLKey(string $key, string $password = null): ClientBuilder
+    public function setSSLKey(string $key, ?string $password = null): ClientBuilder
     {
         $this->sslKey = [$key, $password];
 

src/Elasticsearch/Connections/Connection.php

@@ -174,7 +174,7 @@ public function __construct(
      * @param \Elasticsearch\Transport $transport
      * @return mixed
      */
-    public function performRequest($method, $uri, $params = null, $body = null, $options = [], Transport $transport = null)
+    public function performRequest($method, $uri, $params = null, $body = null, $options = [], ?Transport $transport = null)
     {
         if ($body !== null) {
             $body = $this->serializer->serialize($body);
@@ -226,7 +226,7 @@ public function getLastRequestInfo()
 
     private function wrapHandler(callable $handler)
     {
-        return function (array $request, Connection $connection, Transport $transport = null, $options) use ($handler) {
+        return function (array $request, Connection $connection, ?Transport $transport = null, $options = []) use ($handler) {
 
             $this->lastRequest = [];
             $this->lastRequest['request'] = $request;

src/Elasticsearch/Connections/ConnectionInterface.php

@@ -112,6 +112,6 @@ public function getLastRequestInfo();
      */
 	// @codingStandardsIgnoreStart
 	// "Arguments with default values must be at the end of the argument list" - cannot change the interface
-    public function performRequest(string $method, string $uri, ?array $params = [], $body = null, array $options = [], Transport $transport = null);
+    public function performRequest(string $method, string $uri, ?array $params = [], $body = null, array $options = [], ?Transport $transport = null);
 	// @codingStandardsIgnoreEnd
 }