spawn: try to keep signals blocked in spawned child

While we only want to stop our daemons and gracefully destroy
subprocesses, it is common for 'Ctrl-C' from a terminal to kill
the entire pgroup.

Killing an entire pgroup nukes subprocesses like git-upload-pack
breaks graceful shutdown on long clones.  Make a best effort to
ensure git-upload-pack processes are not broken when somebody
signals an entire process group.

Followup-to: commit 37bf2db81bbbe114d7fc5a00e30d3d5a6fa74de5
("doc: systemd examples should only kill one process")

1 files changed, 1 insertions, 1 deletions

diff --git a/t/spawn.t b/t/spawn.t
index 9e58f675..0f756462 100644
--- a/t/spawn.t
+++ b/t/spawn.t
@@ -87,7 +87,7 @@ use PublicInbox::Spawn qw(which spawn popen_rd);
         is(kill(0, $pid), 1, 'child process is running');
         ok(!defined(sysread($fh, my $buf, 1)) && $!{EAGAIN},
            'sysread returned quickly with EAGAIN');
-        is(kill(15, $pid), 1, 'child process killed early');
+        is(kill(9, $pid), 1, 'child process killed early');
         is(waitpid($pid, 0), $pid, 'child process reapable');
         isnt($?, 0, '$? set properly: '.$?);
 }