flake: export LC_ALL in shell hook to fix ansible-lint

On some systems, the nix development shell based on this flake has a
misconfigured locale, which causes ansible-lint to crash. Exporting the
`LC_ALL` variable fixes the issue (other workarounds are discussed
in NixOS/nixpkgs#223151).

flake.nix

@@ -21,6 +21,7 @@
             pkgs.mkShell {
               shellHook = ''
                 export RUST_SRC_PATH=${pkgs.rustPlatform.rustLibSrc}
+                export LC_ALL="C.UTF-8"
               '';
               nativeBuildInputs = devDeps ++ [ rustc ];
             };