collections/requirements.yml: pin community.docker to >=3.6.0

The Draupnir roles now use `community.docker.docker_image_pull` and
`community.docker.docker_image_build`, both first available in
community.docker 3.6.0 (Jan 2024, shipped with Ansible 9.2.0).

This pin only takes effect for AWX / Automation Platform users (CLI
users do not install collections from this file), but those are the
users most likely to hit the issue with a stale collection cached in
their controller.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/5187.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

collections/requirements.yml

@@ -18,3 +18,8 @@
 collections:
   - name: community.general
   - name: community.docker
+    # `community.docker.docker_image_pull` and `community.docker.docker_image_build`
+    # are used by some roles (e.g. matrix-bot-draupnir,
+    # matrix-appservice-draupnir-for-all) and are first available in
+    # community.docker 3.6.0 (Jan 2024 / Ansible 9.2.0).
+    version: ">=3.6.0"