golang: Switch default to Go1.21

/reviewed-by @kirr and @jerome
/reviewed-on !1494
19 jobs for master in 0 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

00:16:22

passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

00:30:24

failed ERP5.StandaloneDeploymentScriptTest-Debian.Buster.Master

15:02:22

passed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Buster

00:37:02

passed SlapOS.Eggs.UnitTest-Master.Python2

00:16:04

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:50

failed SlapOS.Eggs.UnitTest-Master.Python3Next

00:17:23

failed SlapOS.SoftwareReleases.IntegrationTest-Master

07:56:01

passed SlapOS.Theia.ResilienceTest-Master-ERP5

08:00:48

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

00:28:06

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

15:02:00

passed ERP5.StandaloneDeploymentScriptTest-Debian.Buster

00:40:42

passed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Buster

00:59:43

passed SlapOS.Eggs.UnitTest-Master.Python2

00:24:16

passed SlapOS.Eggs.UnitTest-Master.Python3

00:23:15

failed SlapOS.Eggs.UnitTest-Master.Python3Next

00:26:52

failed SlapOS.SoftwareReleases.IntegrationTest-Master

06:29:37

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster

00:48:22

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

15:02:05