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.

cli/portforward_test.go

@@ -429,11 +429,9 @@ func setupTestListener(t *testing.T, l net.Listener, prefix []byte) string {
 				return
 			}
 
-			wg.Add(1)
-			go func() {
+			wg.Go(func() {
 				echoIfPrefixed(t, c, prefix)
-				wg.Done()
-			}()
+			})
 		}
 	}()
 

cli/ssh_test.go

@@ -1360,12 +1360,10 @@ func TestSSH(t *testing.T) {
 					return
 				}
 
-				wg.Add(1)
-				go func() {
-					defer wg.Done()
+				wg.Go(func() {
 					defer fd.Close()
 					agentssh.Bicopy(ctx, fd, fd)
-				}()
+				})
 			}
 		})
 
@@ -1426,12 +1424,10 @@ func TestSSH(t *testing.T) {
 					return
 				}
 
-				wg.Add(1)
-				go func() {
-					defer wg.Done()
+				wg.Go(func() {
 					defer fd.Close()
 					agentssh.Bicopy(ctx, fd, fd)
-				}()
+				})
 			}
 		})
 
@@ -1576,12 +1572,10 @@ func TestSSH(t *testing.T) {
 						return
 					}
 
-					wg.Add(1)
-					go func() {
-						defer wg.Done()
+					wg.Go(func() {
 						defer fd.Close()
 						agentssh.Bicopy(ctx, fd, fd)
-					}()
+					})
 				}
 			})