make lease more robust

Signed-off-by: Yuchen Liang <yuchen@neon.tech>

libs/pageserver_api/src/models.rs

@@ -181,8 +181,8 @@ impl LsnLease {
     pub const DEFAULT_LENGTH: Duration = Duration::from_secs(10 * 60);
 
     /// Checks whether the lease is expired.
-    pub fn is_expired(&self) -> bool {
-        SystemTime::now() > self.valid_until
+    pub fn is_expired(&self, now: &SystemTime) -> bool {
+        now > &self.valid_until
     }
 }