Bump version to 0.9.0

Let's start the next libportal release cycle.

Author: GeorgesStavracas

meson.build

@@ -1,5 +1,5 @@
 project('libportal','c',
-        version: '0.8.1',
+        version: '0.9.0',
         default_options: ['warning_level=2'],
         meson_version: '>= 0.49.0')