fix(extras/rust): fix config key for files.exclude

It seems like the key changed it's name from `files.excludeDirs` to `files.exclude` at some point.
At least that is the (only) name that can be found in the docs now: https://rust-analyzer.github.io/book/configuration.html (ctrl+f for "files.exclude")

Also add `".jj"` as an excluded directory, which is like `".git"` but for jujutsu (https://jj-vcs.github.io/jj/latest/cli-reference/#jj-git-init).

lua/lazyvim/plugins/extras/lang/rust.lua

@@ -93,9 +93,10 @@ return {
               },
             },
             files = {
-              excludeDirs = {
+              exclude = {
                 ".direnv",
                 ".git",
+                ".jj",
                 ".github",
                 ".gitlab",
                 "bin",