topgrade: gate neovim tarball updater to debian family only

update-neovim.sh and the topgrade [commands] entry that calls it are
only meaningful where neovim is not a distro package. On arch-family
boxes the template renders empty, so chezmoi removes the script
instead of deploying a no-op, and topgrade no longer runs a step that
could fail on unmanaged paths.

dot_config/topgrade/topgrade.toml.tmpl

@@ -31,8 +31,11 @@ repos = [
     "~/Documents/Git/*"
 ]
 
+{{- if eq .os_family "debian" }}
 [commands]
-# Debian-only (script no-ops elsewhere): apt neovim is stale, so debian
-# machines install from the pinned binary tarball. Arch uses pacman.
+# Debian-family-only: apt neovim is stale, so debian machines install from
+# the pinned binary tarball. Arch-family boxes get neovim from pacman/aur,
+# so neither the script nor this entry is deployed there.
 "~/.local/bin/update-neovim.sh" = "neovim"
+{{- end }}
 

dot_local/bin/update-neovim.sh.tmpl

@@ -1,3 +1,4 @@
+{{- if eq .os_family "debian" }}
 #!/usr/bin/env bash
 # =============================================================================
 #  update-neovim.sh — chezmoi-managed, deployed to ~/.local/bin/update-neovim.sh
@@ -66,3 +67,4 @@ sudo ln -sf "/opt/${NVIM_EXTRACT_DIR}/bin/nvim" /usr/local/bin/nvim
 
 echo "neovim $NVIM_TARGET_VERSION installed"
 nvim --version | head -1
+{{- end }}