fix(ci): runs-on self-hosted to match koala runner labels

The koala act_runner has labels [self-hosted, linux, amd64]. The
default ubuntu-latest label doesn't match, so the release workflow
silently produced zero runs on every push. Matches the convention
used by hyperguild + infra workflows.

Runner is offline at time of this commit — bring it up on koala via
the act_runner systemd unit before expecting tags to appear.

[skip-release]

.gitea/workflows/release.yml

@@ -17,7 +17,7 @@ on:
 
 jobs:
   tag:
-    runs-on: ubuntu-latest
+    runs-on: self-hosted
     steps:
       - name: checkout
         uses: actions/checkout@v4