fix(forgejo-runner): use hostname command instead of $HOSTNAME variable

core.func overwrites $HOSTNAME with a formatted emoji string for display
purposes, causing runner registration to send garbled ANSI codes as the
runner name. Use $(hostname) to get the actual system hostname.

install/forgejo-runner-install.sh

@@ -63,7 +63,7 @@ export DOCKER_HOST="unix:///run/podman/podman.sock"
 forgejo-runner register \
   --instance "$FORGEJO_INSTANCE" \
   --token "$FORGEJO_RUNNER_TOKEN" \
-  --name "$HOSTNAME" \
+  --name "$(hostname)" \
   --labels "$RUNNER_LABELS" \
   --no-interactive
 msg_ok "Registered Forgejo Runner"