io_uring: address review nits in BoundedInjectedCompletionsPerEvent

Per ravenblackx review: tighten EXPECT_GE to EXPECT_EQ since the
eventfd is only written by IoUring's self-poke, so the callback fires
exactly 3 times for 3+3+1. Also unify event_callback_invocations to
int32_t for consistency with the other counters.

Author: aburan28

test/common/io/io_uring_impl_test.cc

@@ -283,7 +283,7 @@ TEST_F(IoUringImplTest, BoundedInjectedCompletionsPerEvent) {
   const Event::FileTriggerType trigger = Event::PlatformDefaultTriggerType;
 
   int32_t total_completions = 0;
-  uint32_t event_callback_invocations = 0;
+  int32_t event_callback_invocations = 0;
   std::vector<int32_t> per_invocation_counts;
 
   auto file_event = dispatcher->createFileEvent(
@@ -314,9 +314,11 @@ TEST_F(IoUringImplTest, BoundedInjectedCompletionsPerEvent) {
   waitForCondition(*dispatcher, [&total_completions]() { return total_completions == 7; });
 
   // Each tick after the first must have been driven by the eventfd self-poke since we never
-  // called activate() again — proving the re-arm path works.
+  // called activate() again — proving the re-arm path works. With cap=3 and 7 injected
+  // completions the drain must split exactly 3 + 3 + 1 across three ticks, and the eventfd
+  // is only written by IoUring itself, so the callback is invoked exactly 3 times.
   EXPECT_EQ(7, total_completions);
-  EXPECT_GE(event_callback_invocations, 3u);
+  EXPECT_EQ(3, event_callback_invocations);
   EXPECT_EQ(3, per_invocation_counts[0]);
   EXPECT_EQ(3, per_invocation_counts[1]);
   EXPECT_EQ(1, per_invocation_counts[2]);