Ensure alarm is re-scheduled if timetamp is in the past

Fixes #3672

embassy-nrf/src/time_driver.rs

@@ -209,6 +209,7 @@ impl RtcDriver {
 
         let r = rtc();
 
+        loop {
             let t = self.now();
             if timestamp <= t {
                 // If alarm timestamp has passed the alarm will not fire.
@@ -249,7 +250,12 @@ impl RtcDriver {
                 r.intenclr().write(|w| w.0 = compare_n(n));
             }
 
-        true
+            // If we have not passed the safe timestamp, we can be sure the alarm will be invoked. Otherwise,
+            // we need to retry setting the alarm.
+            if self.now() <= safe_timestamp {
+                return true;
+            }
+        }
     }
 }