golang: v↑ go1.16 (1.16.4 -> 1.16.8)

Going Go1.16.4 -> Go1.16.8 brings in fixes to compiler, runtime and stdlib
including security fixes to net, crypto/tls, archive/zip, math/big, and
net/http/httputil packages:

https://golang.org/doc/devel/release.html#go1.16.minor

Tested on helloworld SR.
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:39

passed SlapOS.Eggs.UnitTest-Master.Python3

00:11:12

passed SlapOS.SlapRunner.ResilienceTest-Master

00:21:48

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:15:36

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

10:26:24

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

10:58:46