Bump version to 3.4.6-rc

The 3.4 branch is EOL and there is no intention to actually release 3.4.6.

But as I'm backporting a few compilation and warning fixes to ensure the
branch still builds on CI and with recent compilers, the version needs to
be updated so it's not wrongly identifying itself as 3.4.5.stable.

version.py

@@ -2,8 +2,8 @@ short_name = "godot"
 name = "Godot Engine"
 major = 3
 minor = 4
-patch = 5
-status = "stable"
+patch = 6
+status = "rc"
 module_config = ""
 year = 2022
 website = "https://godotengine.org"