[#3271] bump version in configure.ac to 2.5.7

Author: andrei-pavel

ChangeLog

@@ -27,7 +27,7 @@ Kea 2.5.6 (development) released on February 28, 2024
 2204.	[func]		tmark
 	The skeleton of a new open source hook library,
 	libdhcp_perfmon.so, has been added.  The library is
-	still in development and does yet provide any functionality.
+	still in development and does not yet provide any functionality.
 	(Gitlab #3242)
 
 Kea 2.5.5 (development) released on January 31, 2024

configure.ac

@@ -6,7 +6,7 @@ AC_PREREQ([2.69])
 # For released versions, this is in x.y.z format.
 # For GIT versions, this is x.y.z-git, where x.y.z denotes the next development
 # version that is worked on and that is to be released.
-AC_INIT(kea, 2.5.6-git, [email protected])
+AC_INIT(kea, 2.5.7-git, [email protected])
 AC_CONFIG_SRCDIR(README)
 
 # serial-tests is not available in automake version before 1.13, so