tests: fix a few fd leaks

We relied on the finalizer to close a few fds.
For some reason, this did not cause problems on Linux,
but on MacOS, it causes unmount failures:

umount(/private/tmp/gocryptfs-test-parent/194654785/default-plain): Resource busy -- try 'diskutil unmount'

1 files changed, 2 insertions, 0 deletions

diff --git a/tests/matrix/matrix_test.go b/tests/matrix/matrix_test.go
index d0ad0d5..d52c3f8 100644
--- a/tests/matrix/matrix_test.go
+++ b/tests/matrix/matrix_test.go
@@ -405,10 +405,12 @@ func TestRmwRace(t *testing.T) {
 	if err != nil {
 		t.Fatalf("file create failed")
 	}
+	defer f1.Close()
 	f2, err := os.Create(fn)
 	if err != nil {
 		t.Fatalf("file create failed")
 	}
+	defer f2.Close()
 
 	oldBlock := bytes.Repeat([]byte("o"), 4096)