refactor: use sync.WaitGroup.Go in tests (#26671)

Migrate `wg.Add(1); go func() { defer wg.Done(); ... }()` to
`wg.Go(func() { ... })` in tests.

Where the prior pattern passed the loop variable explicitly via a
closure parameter (`go func(id int) { ... }(i)`), drop the parameter and
reference the loop variable directly. Per-iteration loop variables since
Go 1.22 make this safe.

aibridge/internal/integrationtest/circuit_breaker_internal_test.go

@@ -474,12 +474,10 @@ func TestCircuitBreaker_HalfOpenMaxRequests(t *testing.T) {
 			responses := make(chan int, totalRequests)
 
 			for i := 0; i < totalRequests; i++ {
-				wg.Add(1)
-				go func() {
-					defer wg.Done()
+				wg.Go(func() {
 					status := doRequest()
 					responses <- status
-				}()
+				})
 			}
 
 			wg.Wait()

aibridge/keypool/keypool_test.go

@@ -619,11 +619,9 @@ func TestKeyConcurrent(t *testing.T) {
 			const numGoroutines = 10
 			var wg sync.WaitGroup
 			for r := range numGoroutines {
-				wg.Add(1)
-				go func(r int) {
-					defer wg.Done()
+				wg.Go(func() {
 					tc.run(r, key)
-				}(r)
+				})
 			}
 			wg.Wait()