fix: do not interrupt threads on cancellation in UniDelayOnItem

This causes spurious interrupt signals in failure retry with exponential backoff
that get propagated downstream.

Also https://twitter.com/relizarov/status/1184460504238100480

Fixes #1436

implementation/src/main/java/io/smallrye/mutiny/operators/uni/UniDelayOnItem.java

@@ -41,7 +41,7 @@ public void cancel() {
             if (!isCancelled()) {
                 super.cancel();
                 if (scheduledFuture != null) {
-                    scheduledFuture.cancel(true);
+                    scheduledFuture.cancel(false);
                 }
             }
         }

implementation/src/test/java/io/smallrye/mutiny/groups/UniOnFailureRetryTest.java

@@ -9,6 +9,7 @@
 import java.time.Duration;
 import java.util.List;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.concurrent.atomic.AtomicReference;
@@ -558,4 +559,21 @@ public void rejectNullExecutors() {
                 .isInstanceOf(IllegalArgumentException.class)
                 .hasMessage("`executor` must not be `null`");
     }
+
+    @Test
+    void avoidSpuriousInterruptsWithBackoff() {
+        AtomicBoolean flip = new AtomicBoolean();
+        AtomicBoolean interrupted = new AtomicBoolean();
+        String result = Uni.createFrom().item(() -> {
+            if (flip.getAndSet(true)) {
+                return "yolo";
+            }
+            throw new RuntimeException("boom");
+        })
+                .onFailure().retry().withBackOff(Duration.ofMillis(100), Duration.ofSeconds(5)).atMost(1)
+                .onItem().invoke(() -> interrupted.set(Thread.currentThread().isInterrupted()))
+                .await().atMost(Duration.ofSeconds(1));
+        assertThat(result).isEqualTo("yolo");
+        assertThat(interrupted).isFalse();
+    }
 }