Update test method to fix test issue:47861 (#49604)

Author: nagilson

test/dotnet.Tests/GivenExponentialRetry.cs

@@ -25,17 +25,18 @@ public async Task ItReturnsOnSuccess()
             retryCount.Should().Be(1);
         }
 
-        [Fact(Skip = "https://github.com/dotnet/sdk/issues/47861")]
+        [Fact]
         public async Task ItRetriesOnError()
         {
             var retryCount = 0;
-            Func<Task<string>> action = () =>
+            Func<Task<string?>> action = () => // Updated to use nullable reference type  
             {
                 retryCount++;
-                throw new Exception();
+                return Task.FromResult<string?>(null); // Updated to match nullable reference type  
             };
-            await Assert.ThrowsAsync<AggregateException>(async () => await ExponentialRetry.ExecuteWithRetryOnFailure<string>(action, 2, timer: () => ExponentialRetry.Timer(ExponentialRetry.TestingIntervals)));
+            var res = await ExponentialRetry.ExecuteWithRetryOnFailure<string?>(action, 2, timer: () => ExponentialRetry.Timer(ExponentialRetry.TestingIntervals));
 
+            res.Should().BeNull();
             retryCount.Should().Be(2);
         }
     }