chore(rootfs/Dockerfile): update Go toolchain to v1.20.12 (#356)

See https://golang.org/doc/devel/release#go1.20.minor

Author: mboersma

rootfs/Dockerfile

@@ -7,7 +7,7 @@ ENV ANSIBLE_VERSION=2.15.8 \
   AZCLI_VERSION=2.52.0 \
   DOCKER_VERSION=20.10.2 \
   ETCDCTL_VERSION=v3.1.8 \
-  GO_VERSION=1.20.10 \
+  GO_VERSION=1.20.12 \
   GOLANGCI_LINT_VERSION=v1.52.2 \
   GOSS_VERSION=v0.3.21 \
   HELM_VERSION=3.11.2 \