github+Docker: bump and fix go version to 1.16.8

There's a race condition in the h2_bundle.go of go 1.17 and later. The
issue golang/go#51799 mentions that this might
be fixed in go 1.19, so we'll need to wait for that.
We make sure we build our docker images with go 1.16.8 to not run into
the issue in the wild.

.github/workflows/main.yml

@@ -19,7 +19,10 @@ env:
 
   # If you change this value, please change it in the following files as well:
   # /Dockerfile
-  GO_VERSION: 1.17.8
+  #
+  # Don't bump this until go 1.19 is out (which should include a fix for
+  # https://github.com/golang/go/issues/51799).
+  GO_VERSION: 1.16.8
 
 jobs:
   ########################

Dockerfile

@@ -1,4 +1,6 @@
-FROM golang:1.15.5-alpine as builder
+# Don't bump this until go 1.19 is out (which should include a fix for
+# https://github.com/golang/go/issues/51799).
+FROM golang:1.16.8-alpine as builder
 
 # Force Go to use the cgo based DNS resolver. This is required to ensure DNS
 # queries required to connect to linked containers succeed.