gtk4: 4.18.6 -> 4.20.1

[aytizren]

A few new versions of gtk4 were released over the past couple of months

Full changelog: https://gitlab.gnome.org/GNOME/gtk/-/compare/4.18.6...4.20.1

Things done

Updated the version and hash for src and added librsvg as a dependency.

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

---

Add a 👍 reaction to pull requests you find important.

[acid-bong]

Due to this PR causing lots of rebuilds, rebase your branch onto staging and point this PR to staging (Edit > Base branch)

[dtomvan]

Could a libadwaita bump maybe get bundled with this PR? The new 1.8.0 depends on gtk4 4.20. Like in #416565

[jtojnar]

Thanks. Though we tend to do major bump of GTK 4 and libadwaita as part of GNOME bumps #440720

[aytizren]

Thanks. Though we tend to do major bump of GTK 4 and libadwaita as part of GNOME bumps #440720

Should this PR be closed in favor of #440720, which would need a bit of work and time to be merged, or should I just bundle a glib and libadwaita update into this PR?

[jtojnar]

There are some breakages that require changes in other packages, which is why we need to bundle major glib builds with other related packages.

[twassman]

Should be closed, as #440720 has been merged.