internal/pkg: override "." for directory checksum

This makes the checksum consistent with the final resting state of artifact directories without incurring the cost of an extra pair of chown syscalls.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/tar_test.go

@@ -35,9 +35,9 @@ func TestTar(t *testing.T) {
 
 				"work": {Mode: fs.ModeDir | 0700},
 			}, pkg.MustDecode(
-				"yJlSb2A3jxaMLuKqwp1GwHOguAHddS9MjygF9ICEeegKfRvgLPdPmNh8mva47f8o",
+				"cTw0h3AmYe7XudSoyEMByduYXqGi-N5ZkTZ0t9K5elsu3i_jNIVF5T08KR1roBFM",
 			))
-		}, pkg.MustDecode("d14kfTvK8uyYIrMq-NUPGGIGmYKcFytmrsvEu5oXibVfmxhu7Y_dAt3rXpsHVSPM")},
+		}, pkg.MustDecode("PrNWkHqtSmdtVecctlI9Xf63dQPIyyLBIMCtRAP2-VqF9u1oQ8ydV7-WPbzEvMkG")},
 
 		{"http expand", nil, func(t *testing.T, base *check.Absolute, c *pkg.Cache) {
 			checkTarHTTP(t, base, c, fstest.MapFS{
@@ -46,9 +46,9 @@ func TestTar(t *testing.T) {
 				"lib":            {Mode: fs.ModeDir | 0700},
 				"lib/libedac.so": {Mode: fs.ModeSymlink | 0777, Data: []byte("/proc/nonexistent/libedac.so")},
 			}, pkg.MustDecode(
-				"rY9_cYWgGWgGI2efznu9RP6bPnjM6I5CHFY2nGysnlbPDdOx_iIaiGKYesmMARwC",
+				"CH3AiUrCCcVOjOYLaMKKK1Da78989JtfHeIsxMzWOQFiN4mrCLDYpoDxLWqJWCUN",
 			))
-		}, pkg.MustDecode("tqrqx8Ig_l9jjDywovatvg3btS-6hf182Ofzpjcrj2148NhobE_Xb7wrYptZoXFD")},
+		}, pkg.MustDecode("YZUoGdMwmfW5sQWto9hQgMKah648rHKck8Ds_GGnqgCBpTAiZKOefpHCKnvktfYh")},
 	})
 }