chore(ci): Remove CI concurrency group & small fixes (#1758)

## Description

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about the "what" this PR is solving -->

It has no effect. The actions are run in parallel anyway. They have been
previously updated to not fail when run in parallel.

## Linked Issues

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## Additional Context

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flake.nix

@@ -44,7 +44,7 @@
             inputsFrom = [ self.packages.${system}.airi ];
             packages = [
               nixd
-              nixfmt-rfc-style
+              nixfmt
               nixfmt-tree
               pnpm
               python314