update containerd binary to v1.6.20

Notable Updates

- Disable looking up usernames and groupnames on host
- Add support for Windows ArgsEscaped images
- Update hcsshim to v0.9.8
- Fix debug flag in shim
- Add WithReadonlyTempMount to support readonly temporary mounts
- Update ttrpc to fix file descriptor leak
- Update runc binary to v1.1.5
= Update image config to support ArgsEscaped

full diff: https://github.com/containerd/containerd/compare/v1.6.19...v1.6.20

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 389e18081dacc6a88e7bb9086afb87ae9ccc62b3)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

hack/dockerfile/install/containerd.installer

@@ -15,7 +15,7 @@ set -e
 # the binary version you may also need to update the vendor version to pick up
 # bug fixes or new APIs, however, usually the Go packages are built from a
 # commit from the master branch.
-: "${CONTAINERD_VERSION:=v1.6.19}"
+: "${CONTAINERD_VERSION:=v1.6.20}"
 
 install_containerd() (
 	echo "Install containerd version $CONTAINERD_VERSION"