Remove async void usage

Remove tests using `async void` that shouldn't be.

test/Polly.Core.Tests/Hedging/HedgingResilienceStrategyTests.cs

@@ -199,7 +199,7 @@ public async Task ExecuteAsync_EnsurePrimaryContextFlows()
     }
 
     [Fact]
-    public async void ExecuteAsync_EnsureHedgedTasksCancelled_Ok()
+    public async Task ExecuteAsync_EnsureHedgedTasksCancelled_Ok()
     {
         // arrange
         _testOutput.WriteLine("ExecuteAsync_EnsureHedgedTasksCancelled_Ok executing...");
@@ -658,7 +658,7 @@ ValueTask<Outcome<string>> BackgroundWork(ResilienceContext resilienceContext)
     }
 
     [Fact]
-    public async void ExecuteAsync_ZeroHedgingDelay_EnsureAllTasksSpawnedAtOnce()
+    public async Task ExecuteAsync_ZeroHedgingDelay_EnsureAllTasksSpawnedAtOnce()
     {
         // arrange
         int executions = 0;

test/Polly.Core.Tests/Retry/RetryResilienceStrategyTests.cs

@@ -209,7 +209,7 @@ public override ITimer CreateTimer(TimerCallback callback, object? state, TimeSp
     }
 
     [Fact]
-    public async void OnRetry_EnsureCorrectArguments()
+    public async Task OnRetry_EnsureCorrectArguments()
     {
         var attempts = new List<int>();
         var delays = new List<TimeSpan>();
@@ -244,7 +244,7 @@ public async void OnRetry_EnsureCorrectArguments()
     }
 
     [Fact]
-    public async void MaxDelay_EnsureRespected()
+    public async Task MaxDelay_EnsureRespected()
     {
         var delays = new List<TimeSpan>();
         _options.OnRetry = args =>

test/Polly.Extensions.Tests/Issues/IssuesTests.PartitionedRateLimiter_1365.cs

@@ -12,7 +12,7 @@ public partial class IssuesTests
     /// Additionally, it also shows how to disable rate limiting for admin users.
     /// </summary>
     [Fact]
-    public async void PartitionedRateLimiter_EnsureUserLimited_1365()
+    public async Task PartitionedRateLimiter_EnsureUserLimited_1365()
     {
         // arrange
         var userKey = new ResiliencePropertyKey<string>("user");