fix(ci): use a valid mirror secret name

.forgejo/workflows/pipeline.yml

@@ -212,11 +212,11 @@ jobs:
 
       - name: Push main to GitHub
         env:
-          GITHUB_MIRROR_SSH_KEY: ${{ secrets.GITHUB_MIRROR_SSH_KEY }}
+          MIRROR_SSH_KEY: ${{ secrets.MIRROR_SSH_KEY }}
         run: |
-          test -n "$GITHUB_MIRROR_SSH_KEY"
+          test -n "$MIRROR_SSH_KEY"
           install -d -m 0700 .ci/mirror
-          printf '%s\n' "$GITHUB_MIRROR_SSH_KEY" >.ci/mirror/id_ed25519
+          printf '%s\n' "$MIRROR_SSH_KEY" >.ci/mirror/id_ed25519
           chmod 0600 .ci/mirror/id_ed25519
           cat >.ci/mirror/known_hosts <<'EOF'
           github.com ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIOMqqnkVzrm0SdG6UOoqKLsabgH5C9okWi0dh2l9GKJl

docs/ci-cd.md

@@ -21,7 +21,7 @@ Forgejo UI:
 - `REGISTRY_USERNAME`: account allowed to push the three Nereus packages.
 - `REGISTRY_PASSWORD`: package-scoped token for that account.
 - `KUBECONFIG_B64`: base64 encoding of a least-privilege deployment kubeconfig.
-- `GITHUB_MIRROR_SSH_KEY`: private half of a write-enabled deploy key for
+- `MIRROR_SSH_KEY`: private half of a write-enabled deploy key for
   `git@github.com:Fi3w0/Nereus.git`.
 
 After registering that deploy key, set the Forgejo Actions repository variable