pump version to :wq2021.09-dev

CHANGELOG

@@ -1,3 +1,5 @@
+Version 2021.09 (unreleased)
+
 Version 2021.07 (2021-07-04)
   Friendica Core
     Updates to the translation DE, EN-GB, HU, IT, JA [translation teams]

VERSION

@@ -1 +1 @@
-2021.07
+2021.09-dev

boot.php

@@ -38,7 +38,7 @@ use Friendica\Util\DateTimeFormat;
 
 define('FRIENDICA_PLATFORM',     'Friendica');
 define('FRIENDICA_CODENAME',     'Siberian Iris');
-define('FRIENDICA_VERSION',      '2021.07');
+define('FRIENDICA_VERSION',      '2021.09-dev');
 define('DFRN_PROTOCOL_VERSION',  '2.23');
 define('NEW_TABLE_STRUCTURE_VERSION', 1288);