test: use saved process PID instead of %%

As the `%%` specifier might fail if the current job (i.e. the last
background job) already finished:

```
[   61.692196] testsuite-04.sh[656]: ++ systemd-id128 new
[   61.705407] testsuite-04.sh[263]: + ID=912cb8f8ef304153a123f772bb0fe9e0
[   61.706318] testsuite-04.sh[657]: + systemd-cat -t 912cb8f8ef304153a123f772bb0fe9e0 bash -c 'echo parent; (echo child) & wait'
[   61.720940] testsuite-04.sh[263]: + PID=657
[   61.721126] testsuite-04.sh[263]: + wait %%
[   61.723014] testsuite-04.sh[263]: /usr/lib/systemd/tests/testdata/units/testsuite-04.sh: line 96: wait: %%: no such job
```

diff --git a/test/units/testsuite-04.sh b/test/units/testsuite-04.sh
index 7521a6d2e5ae8d248b443a4c15267a900e40ee07..b5468cbea40f18367102181d3caabef13bd786c5 100755 (executable)
--- a/test/units/testsuite-04.sh
+++ b/test/units/testsuite-04.sh
@@ -93,7 +93,7 @@ cmp /expected /output
 ID=$(systemd-id128 new)
 systemd-cat -t "$ID" bash -c 'echo parent; (echo child) & wait' &
 PID=$!
-wait %%
+wait $PID
 journalctl --sync
 # We can drop this grep when https://github.com/systemd/systemd/issues/13937
 # has a fix.