archive/zip: add test for Modified vs ModTime behavior

Lock in fix for #22738, submitted in CL 78031.

Fixes #22738.

Change-Id: I6896feb158569e3f12fa7055387cbd7caad29ef4
Reviewed-on: https://go-review.googlesource.com/80635
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

src/archive/zip/writer_test.go

@@ -321,7 +321,7 @@ func testReadFile(t *testing.T, f *File, wt *WriteTest) {
 	if f.Name != wt.Name {
 		t.Fatalf("File name: got %q, want %q", f.Name, wt.Name)
 	}
-	testFileMode(t, wt.Name, f, wt.Mode)
+	testFileMode(t, f, wt.Mode)
 	rc, err := f.Open()
 	if err != nil {
 		t.Fatal("opening:", err)