various: mark files with the usual license tags

For .clang-format and pytest.ini, MIT-0 is used because people might want
to copy those.

shell-completion/zsh/_run0

@@ -1,4 +1,5 @@
 #compdef run0
+# SPDX-License-Identifier: LGPL-2.1-or-later
 
 (( $+functions[_run0_unit_properties] )) ||
 _run0_unit_properties() {

shell-completion/zsh/_sd_bus_address

@@ -1,4 +1,5 @@
 #compdef -value-,DBUS_SESSION_BUS_ADDRESS,-default- -value-,DBUS_SYSTEM_BUS_ADDRESS,-default-
+# SPDX-License-Identifier: LGPL-2.1-or-later
 
 local context state state_descr line
 typeset -A val_args

shell-completion/zsh/_systemd-id128

@@ -1,4 +1,5 @@
 #compdef systemd-id128
+# SPDX-License-Identifier: LGPL-2.1-or-later
 
 local context state state_descr line
 typeset -A opt_args

shell-completion/zsh/_userdbctl

@@ -1,4 +1,5 @@
 #compdef userdbctl
+# SPDX-License-Identifier: LGPL-2.1-or-later
 
 local context state state_descr line
 typeset -A opt_args