[8.x] Do not throw in task enqueued by CancellableRunner (#112780) (#112786)

* Do not throw in task enqueued by CancellableRunner (#112780)

CancellableThreads#excute can throw runtime exception including
cancellation. This does not work with AbstractThrottledTaskRunner which
expects enqueued task to _not_ throw. This PR catches any runtime
exception from CancellableThreads and hand it back to the original
runnable.

Resolves: #112779
(cherry picked from commit e22bef6)

# Conflicts:
#	muted-tests.yml

* Update muted-tests.yml

* Update muted-tests.yml

---------

Co-authored-by: Elastic Machine <[email protected]>

Author: ywangd

x-pack/plugin/snapshot-repo-test-kit/src/main/java/org/elasticsearch/repositories/blobstore/testkit/integrity/RepositoryIntegrityVerifier.java

@@ -934,7 +934,11 @@ public void onResponse(Releasable releasable) {
                         if (cancellableThreads.isCancelled()) {
                             runnable.onFailure(new TaskCancelledException("task cancelled"));
                         } else {
-                            cancellableThreads.execute(runnable::run);
+                            try {
+                                cancellableThreads.execute(runnable::run);
+                            } catch (RuntimeException e) {
+                                runnable.onFailure(e);
+                            }
                         }
                     }
                 }