test: Fix flaky HangTracker deallocated test (#7639)

Author: noahsmartin

Sources/Swift/HangTracker.swift

@@ -76,6 +76,9 @@ final class DefaultHangTracker<T: RunLoopObserver> {
         mainQueueState = .init()
     }
 
+    // It's safe to access mainQueueState here regardless of the thread
+    // because this is the only reference to `self` while
+    // it is being deallocated.
     deinit {
         guard let observer = mainQueueState.observer else {
             return

Tests/SentryTests/Integrations/ANR/HangTrackerTests.swift

@@ -208,6 +208,14 @@ final class HangTrackerTests: XCTestCase {
 
         sut = nil
 
+        // Allow the hang tracker's background thread to finish since it holds
+        // a strong reference while it is running
+        let expectation = XCTestExpectation()
+        queue.async {
+            expectation.fulfill()
+        }
+        wait(for: [expectation])
+        
         XCTAssertNil(weakSut, "Expected observer to be deallocated")
     }