build: Bump minimum Meson version to 0.42.1

build: Bump minimum Meson version to 0.42.1

Otherwise it fails to build with:

  FAILED: gtk/im-ipa@sha/imipa.c.o
  ...
  In file included from ../gtk/gtkintl.h:4:0,
                   from ../modules/input/imipa.c:28:
  /opt/include/glib-2.0/glib/gi18n-lib.h:27:2: error: #error You must
          define GETTEXT_PACKAGE before including gi18n-lib.h. Did you
          forget to include config.h?
   #error You must define GETTEXT_PACKAGE before
           including gi18n-lib.h.  Did you forget to include config.h?
    ^~~~~
  ../modules/input/imipa.c:144:3: error: ‘GETTEXT_PACKAGE’ undeclared
          here (not in a function)
     GETTEXT_PACKAGE,     /* Translation domain */
     ^~~~~~~~~~~~~~~
  ../modules/input/imipa.c:145:4: error: ‘GTK_LOCALEDIR’ undeclared
          here (not in a function)
      GTK_LOCALEDIR,     /* Dir for bindtextdomain (not strictly
              needed for "gtk+") */
      ^~~~~~~~~~~~~