extract_utils: use null work-tree for getting the list of affected files

`git apply --numstat` returns different paths depending on current
working directory:

$ pwd
/home/luk/lineage-22/device/google/bramble
$ git apply --numstat /home/luk/lineage-22/device/google/bramble/bramble/HbmSVManager.patch
46	2	smali/com/android/hbmsvmanager/filter/AmbientFilterFactory.smali
$ pwd
/home/luk/lineage-22/device/google/bramble/bramble
$ git apply --numstat /home/luk/lineage-22/device/google/bramble/bramble/HbmSVManager.patch
46	2	bramble/smali/com/android/hbmsvmanager/filter/AmbientFilterFactory.smali

And because of that __get_apktool_unpack_args() fails due to expecting
path to start with res/, smali/ or be equal to AndroidManifest.xml.

Change-Id: I947c115d61207d7be8280939d8266adda9f49a16

Author: luk1337

extract_utils/fixups_blob.py

@@ -192,7 +192,9 @@ def __get_patches(self, ctx: BlobFixupCtx, module_patches_path: str):
         return patches
 
     def __get_patch_affected_files(self, patch: str) -> List[str]:
-        output = run_cmd(['git', 'apply', '--numstat', patch])
+        output = run_cmd(
+            ['git', '--work-tree', os.devnull, 'apply', '--numstat', patch]
+        )
 
         files = []
         for line in output.strip().splitlines():