tools: improve PhantomData usage

The ticket doesn't contain a `T`, it's stringified. We only
produce a new T when verifying.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

pbs-tools/src/ticket.rs

@@ -53,7 +53,7 @@ where
     data: String,
     time: i64,
     signature: Option<Vec<u8>>,
-    _type_marker: PhantomData<T>,
+    _type_marker: PhantomData<fn() -> T>,
 }
 
 impl<T> Ticket<T>