Fix CI failure introduced in commit 851f6649cc.

Fix CI failure introduced in commit 851f6649cc.

The test added in commit 851f6649cc uses a backup taken from a node
created by the previous test to perform standby related checks. On
Windows, however, the standby failed to start with the following error:
FATAL:  could not rename file "backup_label" to "backup_label.old": Permission denied

This occurred because some background sessions from the earlier test were
still active. These leftover processes continued accessing the parent
directory of the backup_label file, likely preventing the rename and
causing the failure. Ensuring that these sessions are cleanly terminated
resolves the issue in local testing.

Additionally, the has_restoring => 1 option has been removed, as it was
not required by the new test.

Reported-by: Robert Haas <robertmhaas@gmail.com>
Backpatch-through: 17
Discussion: https://postgr.es/m/CA+TgmobdVhO0ckZfsBZ0wqDO4qHVCwZZx8sf=EinafvUam-dsQ@mail.gmail.com