fix(extras/rust): fix config key for files.exclude (#5664)

## Description

It seems like the key changed its 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).

---

As an aside, `cargo.loadOutDirsFromCheck` also does not seem to exist
(anymore). But I don't know more about that option, so I haven't touched
it in this PR.

## Related Issue(s)

Not sure if any.

## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

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

@@ -87,9 +87,10 @@ return {
               enable = true,
             },
             files = {
-              excludeDirs = {
+              exclude = {
                 ".direnv",
                 ".git",
+                ".jj",
                 ".github",
                 ".gitlab",
                 "bin",