[release/9.0-staging] Wait to complete the test before releasing the agile reference. (#129430)

Backport of #112387 to release/9.0-staging

/cc @AaronRobinsonMSFT @jkoritzinsky

Closes #129421

## Customer Impact

- [ ] Customer reported
- [x] Found internally

This is flaky test issue that is impacting the 9.0 branch. It was fixed
in 10, but missed 11.

## Regression

- [ ] Yes
- [x] No

Flaky test.

## Testing

This fix has been in 10 and 11 with no further issues.

## Risk

Zero as it has no impact to the product.

Co-authored-by: Jeremy Koritzinsky <jekoritz@microsoft.com>

Author: github-actions[bot]

src/tests/Interop/COM/ComWrappers/API/Program.cs

@@ -1084,6 +1084,7 @@ public unsafe void CrossApartmentQueryInterface_NoDeadlock()
 
                 staThread.Start();
                 mtaThread.Start();
+                testCompleted.WaitOne();
             }
             finally
             {
@@ -1092,8 +1093,6 @@ public unsafe void CrossApartmentQueryInterface_NoDeadlock()
                     Marshal.Release(agileReference);
                 }
             }
-
-            testCompleted.WaitOne();
         }
 
         [DllImport("ole32.dll")]