Fix ITestSkippedEventReceiver not firing for [Skip]-attributed tests

RegisterReceivers was only called inside PrepareTest, which runs after
skip checks. When a test was skipped via [Skip("...")] attribute, the
EventReceiverRegistry global flags were never set, causing the
InvokeTestSkippedEventReceiversAsync fast-path to short-circuit.

Move RegisterReceivers call to ExecuteTestInternalAsync before any skip
checks so attribute-based event receivers are registered early enough
for OnTestSkipped to fire.

Fixes #5252

TUnit.Engine/Services/TestExecution/TestCoordinator.cs

@@ -61,6 +61,10 @@ private async ValueTask ExecuteTestInternalAsync(AbstractExecutableTest test, Ca
 
             _contextRestorer.RestoreContext(test);
 
+            // Register event receivers early so that skip event receivers work
+            // even when the test is skipped before full initialization.
+            _eventReceiverOrchestrator.RegisterReceivers(test.Context, cancellationToken);
+
             // Check if test was already marked as skipped during registration
             // (e.g., by a derived SkipAttribute evaluated in OnTestRegistered).
             // This must be checked before any instance creation or retry/timeout logic.