[lldb-dap] Make TestDAP_Progress more resilient (again)

Before #134048, TestDAP_Progress would wait up to 15 seconds before
checking whether the events came in. Now the test is a lot faster, but
we risk checking the events before they've all arrived. Make up to 10
attempts to find the end event, with a 100ms sleep in between, giving
the test up to a second for the event to arrive after it has been
broadcast.

Author: JDevlieghere

lldb/test/API/tools/lldb-dap/progress/TestDAP_Progress.py

@@ -12,17 +12,31 @@
 
 
 class TestDAP_progress(lldbdap_testcase.DAPTestCaseBase):
+    MAX_ATTEMPS = 10
+
     def verify_progress_events(
         self,
         expected_title,
         expected_message=None,
         expected_not_in_message=None,
         only_verify_first_update=False,
     ):
-        self.assertTrue(len(self.dap_server.progress_events) > 0)
+        # Make up to 10 attempts (= 1 second) for the end event to arrive.
+        end_found = False
+        for _ in range(self.MAX_ATTEMPS):
+            for event in self.dap_server.progress_events:
+                event_type = event["event"]
+                if "progressEnd" in event_type:
+                    end_found = True
+                    break
+            # Wait 100ms before checking again.
+            time.sleep(0.10)
+        self.assertTrue(end_found)
+
+        # Make sure we found the start and update event. If we got this far, we
+        # already know we got an end event.
         start_found = False
         update_found = False
-        end_found = False
         for event in self.dap_server.progress_events:
             event_type = event["event"]
             if "progressStart" in event_type:
@@ -38,12 +52,11 @@ def verify_progress_events(
                 if expected_not_in_message is not None:
                     self.assertNotIn(expected_not_in_message, message)
                 update_found = True
-            if "progressEnd" in event_type:
-                end_found = True
 
         self.assertTrue(start_found)
         self.assertTrue(update_found)
-        self.assertTrue(end_found)
+
+        # Clear the progress events.
         self.dap_server.progress_events.clear()
 
     @skipIfWindows