modules/gnome: use itertools.chain instead of list concatenation

This is better as it avoids building unnecessary lists, and two fixes
the typing issue from concatenating lists of different types.

mesonbuild/modules/gnome.py

@@ -16,6 +16,7 @@
 functionality such as gobject-introspection, gresources and gtk-doc'''
 
 import copy
+import itertools
 import functools
 import os
 import subprocess
@@ -1106,7 +1107,7 @@ class GnomeModule(ExtensionModule):
         scan_command += scan_cflags
         scan_command += ['--cflags-end']
         scan_command += state.get_include_args(inc_dirs)
-        scan_command += state.get_include_args(list(gi_includes) + gir_inc_dirs + inc_dirs, prefix='--add-include-path=')
+        scan_command += state.get_include_args(itertools.chain(gi_includes, gir_inc_dirs, inc_dirs), prefix='--add-include-path=')
         scan_command += list(scan_internal_ldflags)
         scan_command += self._scan_gir_targets(state, girtargets)
         scan_command += self._scan_langs(state, [lc[0] for lc in langs_compilers])