fix git-sync-deps

We really do use this.

Change-Id: I0defcf8aa3b23eec89b38b6720228daa8d50c27b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/394956
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Eric Boren <borenet@google.com>

tools/git-sync-deps

@@ -173,7 +173,7 @@ def git_checkout_to_directory(git, repo, commithash, directory, verbose):
 def parse_file_to_dict(path):
   dictionary = {}
   with open(path) as f:
-    exec(f.read(), dictionary)
+    exec('def Var(x): return vars[x]\n' + f.read(), dictionary)
   return dictionary