use new proxmox-async crate

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

src/bin/proxmox-backup-api.rs

@@ -21,7 +21,7 @@ use proxmox_backup::config;
 fn main() {
     proxmox_backup::tools::setup_safe_path_env();
 
-    if let Err(err) = pbs_runtime::main(run()) {
+    if let Err(err) = proxmox_async::runtime::main(run()) {
         eprintln!("Error: {}", err);
         std::process::exit(-1);
     }