Bump golang.org/x/net from 0.25.0 to 0.38.0 in /src/book01/ch04/go

Bumps [golang.org/x/net](https://github.com/golang/net) from 0.25.0 to 0.38.0.
- [Commits](golang/net@v0.25.0...v0.38.0)

---
updated-dependencies:
- dependency-name: golang.org/x/net
  dependency-version: 0.38.0
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

src/book01/ch04/go/go.mod

@@ -1,10 +1,10 @@
 module ping
 
-go 1.22.3
+go 1.23.0
 
 require github.com/tatsushid/go-fastping v0.0.0-20160109021039-d7bb493dee3e
 
 require (
-	golang.org/x/net v0.25.0 // indirect
-	golang.org/x/sys v0.20.0 // indirect
+	golang.org/x/net v0.38.0 // indirect
+	golang.org/x/sys v0.31.0 // indirect
 )