[master] update to go1.21.3

[thaJeztah]

go1.21.3 (released 2023-10-10) includes a security fix to the net/http package. See the Go 1.21.3 milestone on our issue tracker for details:

https://github.com/golang/go/issues?q=milestone%3AGo1.21.3+label%3ACherryPickApproved

full diff: golang/go@go1.21.2...go1.21.3

From the security mailing:

[security] Go 1.21.3 and Go 1.20.10 are released

Hello gophers,

We have just released Go versions 1.21.3 and 1.20.10, minor point releases.

These minor releases include 1 security fixes following the security policy:

• net/http: rapid stream resets can cause excessive work

  A malicious HTTP/2 client which rapidly creates requests and
  immediately resets them can cause excessive server resource consumption.
  While the total number of requests is bounded to the
  http2.Server.MaxConcurrentStreams setting, resetting an in-progress
  request allows the attacker to create a new request while the existing
  one is still executing.

  HTTP/2 servers now bound the number of simultaneously executing
  handler goroutines to the stream concurrency limit. New requests
  arriving when at the limit (which can only happen after the client
  has reset an existing, in-flight request) will be queued until a
  handler exits. If the request queue grows too large, the server
  will terminate the connection.

  This issue is also fixed in golang.org/x/net/http2 v0.17.0,
  for users manually configuring HTTP/2.

  The default stream concurrency limit is 250 streams (requests)
  per HTTP/2 connection. This value may be adjusted using the
  golang.org/x/net/http2 package; see the Server.MaxConcurrentStreams
  setting and the ConfigureServer function.

  This is CVE-2023-39325 and Go issue https://go.dev/issue/63417.
  This is also tracked by CVE-2023-44487.