Update Go to 1.16.3

go1.16.3 (released 2021/04/01) includes fixes to the compiler, linker, runtime,
the go command, and the testing and time packages. See the Go 1.16.3 milestone
on our issue tracker for details:

https://github.com/golang/go/issues?q=milestone%3AGo1.16.3+label%3ACherryPickApproved

full diff: https://github.com/golang/go/compare/go1.16.2...go1.16.3

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

.zuul/playbooks/containerd-build/run.yaml

@@ -2,7 +2,7 @@
   become: yes
   roles:
   - role: config-golang
-    go_version: '1.16.2'
+    go_version: '1.16.3'
     arch: arm64
   tasks:
   - name: Build containerd