.github/compose/ci.bst-artifact-server.yml: Drop workaround

The incompability with Click 8.0 has been fixed in bst-artifact-server.
Drop the workaround of explicitly specifying `--log-level`.
diff --git a/.github/compose/ci.bst-artifact-server.yml b/.github/compose/ci.bst-artifact-server.yml
index 4eb2468..fbed777 100644
--- a/.github/compose/ci.bst-artifact-server.yml
+++ b/.github/compose/ci.bst-artifact-server.yml
@@ -20,7 +20,6 @@
   controller:
     image: buildstream/buildstream:nightly
     command: ["bst-artifact-server",
-      "--log-level", "warning",
       "--port", "50052",
       "--enable-push",
       "/artifacts"