zfs: the keeper tests make their socket directory in the test's own temporary directory

The group's check failed TestOnlyRootOpensTheKeepersSocketAndANeedlessKeeperIsTheBusDown and TestAKeeperThatDoesNotAnswerIsWarnedOnce: stat /var/tmp: no such file or directory.

Builds: design 42 zfs-owns-zfs §18, A-37

modules/zfs/cmd/zfs-tools/keeper_test.go

@@ -73,7 +73,7 @@ func TestOnlyRootOpensTheKeepersSocketAndANeedlessKeeperIsTheBusDown(t *testing.
 	k := &Keeper{Emit: func(string, any) error { return nil }, States: st,
 		Call:   func(string, any) (json.RawMessage, error) { return nil, errors.New("down") },
 		PeerOf: func(net.Conn) (int, error) { return uid, nil }}
-	dir, err := os.MkdirTemp("/var/tmp", "zk")
+	dir, err := os.MkdirTemp("", "zk")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -148,7 +148,7 @@ func TestOnlyRootOpensTheKeepersSocketAndANeedlessKeeperIsTheBusDown(t *testing.
 // A-37: a root process whose keeper does not answer acts as with the bus down and says so, once, in a warning, for the
 // hand acts, the forgetting of applied keys and the pause alike.
 func TestAKeeperThatDoesNotAnswerIsWarnedOnce(t *testing.T) {
-	dir, err := os.MkdirTemp("/var/tmp", "keeper-down")
+	dir, err := os.MkdirTemp("", "keeper-down")
 	if err != nil {
 		t.Fatal(err)
 	}