net: fix deadlock in lookupProtocol on Windows

If the context expires before `acquireThread(ctx)` succeeds, then the goroutine can block like:

```
net.lookupProtocol.func1()
	C:/hostedtoolcache/windows/go/1.24.1/x64/src/net/lookup_windows.go:58 +0x105
created by net.lookupProtocol in goroutine 2834
	C:/hostedtoolcache/windows/go/1.24.1/x64/src/net/lookup_windows.go:56 +0xda
```

We saw this in our UTs with a leak detector, confirmed by inspection of the source code.

Author: spikecurtis

src/net/lookup_windows.go

@@ -52,7 +52,7 @@ func lookupProtocol(ctx context.Context, name string) (int, error) {
 		proto int
 		err   error
 	}
-	ch := make(chan result) // unbuffered
+	ch := make(chan result, 1) // buffer so that next goroutine never blocks
 	go func() {
 		if err := acquireThread(ctx); err != nil {
 			ch <- result{err: mapErr(err)}
@@ -62,10 +62,7 @@ func lookupProtocol(ctx context.Context, name string) (int, error) {
 		runtime.LockOSThread()
 		defer runtime.UnlockOSThread()
 		proto, err := getprotobyname(name)
-		select {
-		case ch <- result{proto: proto, err: err}:
-		case <-ctx.Done():
-		}
+		ch <- result{proto: proto, err: err}
 	}()
 	select {
 	case r := <-ch: