Bump major version number

meson.build

@@ -2,7 +2,7 @@
 # It is not used when building Dynare as a whole.
 
 project('dynare-preprocessor', 'cpp',
-        version : '6-unstable',
+        version : '7-unstable',
         # NB: update C++ standard in .clang-format whenever the following is modified
         default_options : [ 'cpp_std=gnu++20', 'warning_level=2' ],
         meson_version : '>=0.64.0')