prepare for new release

Author: Byron

VERSION

@@ -1 +1 @@
-3.1.56
+3.1.57

doc/source/changes.rst

@@ -2,6 +2,20 @@
 Changelog
 =========
 
+3.1.57
+======
+
+A security fix for
+
+* https://github.com/gitpython-developers/GitPython/security/advisories/GHSA-3f7w-8rr8-f37f
+* https://github.com/gitpython-developers/GitPython/security/advisories/GHSA-539m-9xh6-q6rr
+
+If you can, also try and provide feedback on the upcoming v4 branch
+https://github.com/gitpython-developers/GitPython/pull/2177 - patches welcome.
+
+See the following for all changes.
+https://github.com/gitpython-developers/GitPython/releases/tag/3.1.55
+
 3.1.56
 ======