build: bump meson version to 0.56.0

Fixes this warning:

    WARNING: Project targeting '>=0.54.0' but tried to use feature introduced in '0.56.0': variables as dictionary.

Fixes: 6f873078d4 ("build: use dictionnary for features instead of configuration_data")

meson.build

@@ -3,7 +3,7 @@ project(
 	'c',
 	version: '0.12.0',
 	license: 'MIT',
-	meson_version: '>=0.54.0',
+	meson_version: '>=0.56.0',
 	default_options: [
 		'c_std=c11',
 		'warning_level=2',