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.

component/golang/buildout.cfg

@@ -53,8 +53,8 @@ environment-extra =
 
 [golang1.16]
 <= golang-common
-url = https://golang.org/dl/go1.16.4.src.tar.gz
-md5sum = 5884a4cb49067b9bcf6e69a1ef44259c
+url = https://golang.org/dl/go1.16.8.src.tar.gz
+md5sum = 92e69a5e1bb6ea5e7498d12d03160032
 
 # go1.16 needs go1.4 to bootstrap
 environment-extra =