Bump version to 4.3-stable \o/

This release turned out to be a massive one, exceeding our original
plans for the development cycle, but for good reasons to address many
critical issues that users identified since the 4.0 release.

The user experience should be much stabler and more polished than in
previous releases, with less obscure and game or workflow-breaking
bugs. And of course the feature set kept increasing with a number of
highly awaited improvements to all engine areas.

We have close to 3500 commits in this release, twice as many as 4.2!

More than 500 contributors were involved in this new feature release,
and we want to thank them all for their amazing contributors, as well
as all users who sponsor the Development Fund, reported bugs, opened
proposals, or supported each other on our community platforms.

version.py

@@ -3,7 +3,7 @@
 major = 4
 minor = 3
 patch = 0
-status = "rc"
+status = "stable"
 module_config = ""
 website = "https://godotengine.org"
-docs = "latest"
+docs = "4.3"