ci: drop redundant docker.sock mount in build-web-image

First real run of the new job failed at container creation:
"Error response from daemon: Duplicate mount point: /var/run/docker.sock".
The docker-build runner's config.yaml has docker_host: "" (not "-"),
which means act_runner already auto-injects the host socket into job
containers on its own - the workflow's explicit
container.volumes mount for the same path was a second, conflicting
request for it. Just dropping the explicit mount; the runner already
provides it.

.gitea/workflows/coder-templates.yml

@@ -37,10 +37,11 @@ on:
 
 jobs:
   build-web-image:
+    # The docker-build runner's docker_host: "" setting already auto-injects
+    # /var/run/docker.sock into job containers - an explicit
+    # container.volumes mount for the same path here fails at container
+    # creation with "Duplicate mount point: /var/run/docker.sock".
     runs-on: docker-build
-    container:
-      volumes:
-        - /var/run/docker.sock:/var/run/docker.sock
     steps:
       - name: Checkout
         uses: actions/checkout@v4