Update CHANGELOG for 5.3.6

Author: fabpot

CHANGELOG-5.3.md

@@ -7,6 +7,14 @@ in 5.3 minor versions.
 To get the diff for a specific change, go to https://github.com/symfony/symfony/commit/XXX where XXX is the change hash
 To get the diff between two versions, go to https://github.com/symfony/symfony/compare/v5.3.0...v5.3.1
 
+* 5.3.6 (2021-07-29)
+
+ * bug #42307 [Mailer] Fixed decode exception when sendgrid response is 202 (rubanooo)
+ * bug #42296 [Dotenv][Yaml] Remove PHP 8.0 polyfill (derrabus)
+ * bug #42274 [VarDumper] `HtmlDumper::setDumpHeader()` accepts `null` (rrpadilla)
+ * bug #42289 [HttpFoundation] Fixed type mismatch (Toflar)
+ * bug #42259 [Security] fix Check if it has session before getSession() (mousezheng)
+
 * 5.3.5 (2021-07-27)
 
  * bug #42270 [WebProfilerBundle] [WebProfiler] "empty" filter bugfix. Filter with name "empty" is not … (luzrain)