Use Debian 11 in Linux_ARMv6 release build task

`DistTasks.yml` contains the tasks used to produce the release builds of the project for each of the host targets. The
builds are produced in Docker containers.

A regression was introduced in the `Linux_ARMv6` task at the time the project's Go version was bumped to 1.21.5. This
task must use a specific version of Debian in the container, which is defined via the image tag. Previously, Debian 10
was used, and a tag of the Go 1.18.3 image was available for this Debian version. However, the maintainers of the image
did not produce a Debian 10 variant of the Go 1.21.5 image, so the use of that tag caused the task to fail:

```
Unable to find image 'docker.elastic.co/beats-dev/golang-crossbuild:1.21.5-armel-debian10' locally
docker: Error response from daemon: manifest for docker.elastic.co/beats-dev/golang-crossbuild:1.21.5-armel-debian10 not found: manifest unknown: manifest unknown.
See 'docker run --help'.
task: Failed to run task "dist:Linux_ARMv6": exit status 125
```

A Debian 11 variant of the image is available, and this version of Debian is also suitable for release builds. So the
solution is to update the image tag referenced in the task to the Debian 11 tag.

Author: per1234

Diff for: DistTasks.yml

@@ -172,7 +172,7 @@ tasks:
       #
       # Until there is a fix released we must use a recent gcc for Linux_ARMv6 build, so for this
       # build we select the debian10 based container.
-      CONTAINER_TAG: "{{.GO_VERSION}}-armel-debian10"
+      CONTAINER_TAG: "{{.GO_VERSION}}-armel-debian11"
       PACKAGE_PLATFORM: "Linux_ARMv6"
       PACKAGE_NAME: "{{.PROJECT_NAME}}_{{.VERSION}}_{{.PACKAGE_PLATFORM}}.tar.gz"