Fixed not mapping sdk_sandbox key to vendor key

Some apps are signed with default sdk_sandbox key.
It results in failure of GtsPackageSignatureTest

Bug: 318798881
Test: run gts -m GtsPackageSignatureTest
Change-Id: I676f48eb2844866f4e61af60d78026a87303d15a
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index 4356394..7b497c1 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -1137,6 +1137,7 @@
           devkeydir + "/shared":   d + "/shared",
           devkeydir + "/platform": d + "/platform",
           devkeydir + "/networkstack": d + "/networkstack",
+          devkeydir + "/sdk_sandbox": d + "/sdk_sandbox",
       })
     else:
       OPTIONS.key_map[s] = d