Fix rust-analyzer startup issue in single-file worktrees (#39441)

I'm not sure about the exact conditions for reproducing this issue, but
whenever I build Zed locally and have it open a single-file worktree on
launch, the rust-analyzer language server fails to start up because Zed
attempts to run `rust-analyzer --help` on a path that is not a
directory. This fixes that by running the command on the parent path in
the case of a single-file worktree.

Release Notes:

- Fixed rust-analyzer startup issue in single-file worktrees

crates/project/src/lsp_store.rs

@@ -12757,7 +12757,10 @@ impl LspAdapterDelegate for LocalLspAdapterDelegate {
 
     #[cfg(not(target_os = "windows"))]
     async fn which(&self, command: &OsStr) -> Option<PathBuf> {
-        let worktree_abs_path = self.worktree.abs_path();
+        let mut worktree_abs_path = self.worktree_root_path().to_path_buf();
+        if self.fs.is_file(&worktree_abs_path).await {
+            worktree_abs_path.pop();
+        }
         let shell_path = self.shell_env().await.get("PATH").cloned();
         which::which_in(command, shell_path.as_ref(), worktree_abs_path).ok()
     }
@@ -12771,7 +12774,10 @@ impl LspAdapterDelegate for LocalLspAdapterDelegate {
     }
 
     async fn try_exec(&self, command: LanguageServerBinary) -> Result<()> {
-        let working_dir = self.worktree_root_path();
+        let mut working_dir = self.worktree_root_path().to_path_buf();
+        if self.fs.is_file(&working_dir).await {
+            working_dir.pop();
+        }
         let output = util::command::new_smol_command(&command.path)
             .args(command.arguments)
             .envs(command.env.clone().unwrap_or_default())