meson.build: add "check: true" for the command that creates __init__.py

Meson warns about this when the "check" keyword is absent,

  WARNING: You should add the boolean check kwarg to the run_command call.
           It currently defaults to false,
           but it will default to true in future releases of meson.
           See also: mesonbuild/meson#9300

and the command should indeed succeed, so we now pass "check: true" to
run_command().

meson.build

@@ -210,6 +210,6 @@ for path in file_paths:
         f.write(content)
   ''',
 ]
-run_command(create_files_command)
+run_command(create_files_command, check: true)
 
 subdir('src')