update to go1.21.6, go1.20.13

go1.21.6 (released 2024-01-09) includes fixes to the compiler, the runtime, and
the crypto/tls, maps, and runtime/pprof packages. See the Go 1.21.6 milestone on
our issue tracker for details:

- https://github.com/golang/go/issues?q=milestone%3AGo1.21.6+label%3ACherryPickApproved
- full diff: https://github.com/golang/go/compare/go1.21.5...go1.21.6

go1.20.13 (released 2024-01-09) includes fixes to the runtime and the crypto/tls
package. See the Go 1.20.13 milestone on our issue tracker for details:

- https://github.com/golang/go/issues?q=milestone%3AGo1.20.13+label%3ACherryPickApproved
- full diff: https://github.com/golang/go/compare/go1.20.12...go1.20.13

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Vagrantfile

@@ -104,7 +104,7 @@ EOF
   config.vm.provision "install-golang", type: "shell", run: "once" do |sh|
     sh.upload_path = "/tmp/vagrant-install-golang"
     sh.env = {
-        'GO_VERSION': ENV['GO_VERSION'] || "1.21.5",
+        'GO_VERSION': ENV['GO_VERSION'] || "1.21.6",
     }
     sh.inline = <<~SHELL
         #!/usr/bin/env bash