test: ensure directory exists before creating symlinks

01:42:08 I: Masking supporting services
01:42:08 ln: failed to create symbolic link '/var/tmp/systemd-test-TEST-24-CRYPTSETUP_3/root/etc/systemd/system/systemd-hwdb-update.service': No such file or directory

Author: bluca

test/test-functions

@@ -2024,6 +2024,7 @@ setup_basic_dirs() {
 
 mask_supporting_services() {
     # mask some services that we do not want to run in these tests
+    mkdir -p "$initdir/etc/systemd/system/"
     ln -fsv /dev/null "${initdir:?}/etc/systemd/system/systemd-hwdb-update.service"
     ln -fsv /dev/null "$initdir/etc/systemd/system/systemd-journal-catalog-update.service"
     ln -fsv /dev/null "$initdir/etc/systemd/system/systemd-networkd.service"