maint: Bump version for pre-release (see etc/HACKING.md)

* configure.ac (AC_INIT): Bump version.
(OCTAVE_PATCH_VERSION): Set to 1 for stabilization period before full release.
(OCTAVE_RELEASE_DATE): Update.

configure.ac

@@ -27,7 +27,7 @@ dnl
 
 ### Initialize Autoconf
 AC_PREREQ([2.65])
-AC_INIT([GNU Octave], [9.0.0], [https://octave.org/bugs.html], [octave],
+AC_INIT([GNU Octave], [9.0.1], [https://octave.org/bugs.html], [octave],
         [https://www.gnu.org/software/octave/])
 
 ### Declare version numbers
@@ -41,14 +41,14 @@ dnl AC_INIT requires it to be static, not computed from shell variables.
 
 OCTAVE_MAJOR_VERSION=9
 OCTAVE_MINOR_VERSION=0
-OCTAVE_PATCH_VERSION=0
+OCTAVE_PATCH_VERSION=1
 
 dnl PACKAGE_VERSION is set by the AC_INIT VERSION argument.
 OCTAVE_VERSION="$PACKAGE_VERSION"
 
 OCTAVE_COPYRIGHT="Copyright (C) 1993-2023 The Octave Project Developers."
 
-OCTAVE_RELEASE_DATE="2023-04-13"
+OCTAVE_RELEASE_DATE="2023-11-22"
 
 ## The "API version" is used as a way of checking that interfaces in the
 ## liboctave and libinterp libraries haven't changed in a backwardly