[20.10] vendor: update containerd to latest of docker-20.10 branch

This brings the containerd vendoring up-to-date with the latest changes from
the docker-20.10 branch in our fork (https://github.com/moby/containerd). This
adds some fixes that were included in another fork that was used in the BuildKit
repository, which have now been ported to our fork as well.

Relevant changes:

- docker: avoid concurrent map access panic
- overlay: support "userxattr" option (kernel 5.11) (does not affect vendored code)

full diff: 7cfa023d95...96c5ae04b6

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

vendor.conf

@@ -132,7 +132,7 @@ github.com/googleapis/gax-go                        bd5b16380fd03dc758d11cef74ba
 google.golang.org/genproto                          3f1135a288c9a07e340ae8ba4cc6c7065a3160e8
 
 # containerd
-github.com/containerd/containerd                    7cfa023d95d37076d5ab035003d4839f4b6ba791 https://github.com/moby/containerd.git # master (v1.5.0-dev) + patch for CVE-2021-41190 and CVE-2022-24769
+github.com/containerd/containerd                    96c5ae04b6784e180aaeee50fba715ac448ddb0d https://github.com/moby/containerd.git # docker-20.10 branch
 github.com/containerd/fifo                          0724c46b320cf96bb172a0550c19a4b1fca4dacb
 github.com/containerd/continuity                    5ad51c7aca47b8e742f5e6e7dc841d50f5f6affd # v0.3.0
 github.com/containerd/cgroups                       b9de8a2212026c07cec67baf3323f1fc0121e048 # v1.0.1 

vendor/github.com/containerd/containerd/remotes/docker/resolver.go

@@ -521,7 +521,10 @@ func (r *request) do(ctx context.Context) (*http.Response, error) {
 	if err != nil {
 		return nil, err
 	}
-	req.Header = r.header
+	req.Header = http.Header{} // headers need to be copied to avoid concurrent map access
+	for k, v := range r.header {
+		req.Header[k] = v
+	}
 	if r.body != nil {
 		body, err := r.body()
 		if err != nil {