test-debugruntest: fix on windows

Summary:
On Windows the permission bits are different:

```
 --- test-debugruntest.t
+++ test-debugruntest.t.err
@@ -312,11 +312,11 @@
   $ mkdir dir
   $ touch dir/foo dir/bar
   $ ls -l dir
-  -rw-r--r-- bar
-  -rw-r--r-- foo
+  -rw-rw-rw- bar
+  -rw-rw-rw- foo
```

Reviewed By: sggutier

Differential Revision: D71665132

fbshipit-source-id: 0ba1229bef0070d1c1cc7bb57756f33227b94775

Author: quark-zju

eden/scm/tests/test-debugruntest.t

@@ -312,11 +312,11 @@ ls -l behavior
   $ mkdir dir
   $ touch dir/foo dir/bar
   $ ls -l dir
-  -rw-r--r-- bar
-  -rw-r--r-- foo
+  -rw....... bar (re)
+  -rw....... foo (re)
   $ cd dir
   $ ls -l
-  -rw-r--r-- bar
-  -rw-r--r-- foo
+  -rw....... bar (re)
+  -rw....... foo (re)
   $ cd