Change dbus call from GetUnit to LoadUnit as GetUnit doesn't work reliably

src/provider/systemdmanager/manager.rs

@@ -356,8 +356,11 @@ impl SystemdManager {
     }
 
     pub fn is_running(&self, unit: &str) -> Result<bool, anyhow::Error> {
+        // We are using `LoadUnit` here, as GetUnit can fail seemingly at random, when the unit
+        // is not loaded due to systemd garbage collection.
+        // see https://github.com/systemd/systemd/issues/1929 for more information
         let unit_node = self
-            .method_call("GetUnit", (&unit,))
+            .method_call("LoadUnit", (&unit,))
             .map(|r: (Path,)| r.0)?;
 
         let proxy = self