golang: v↑ go1.15 (1.15.8 -> 1.15.10)

Going Go1.15.8 -> Go1.15.10 brings in fixes to compiler, runtime and stdlib
including security fixes to archive/zip and encoding/xml:

https://golang.org/doc/devel/release.html#go1.15.minor

Tested on helloworld SR (by adjusting it to use go1.15 instead of go1.16).

component/golang/buildout.cfg

@@ -62,8 +62,8 @@ environment-extra =
 
 [golang1.15]
 <= golang-common
-url = https://golang.org/dl/go1.15.8.src.tar.gz
-md5sum = 7e4b8580bfe25ffc51501b1dc3d2d8ce
+url = https://golang.org/dl/go1.15.10.src.tar.gz
+md5sum = 898a4aea4bf5d4adc924154e347acfa3
 
 # go1.15 needs go1.4 to bootstrap
 environment-extra =