[release] Work-around deps-processing problem

TBR=tmrts@chromium.org

No-Try: true
Bug: chromium:1106435
Change-Id: I52657b4ee924e5e0133b0784bc12a0d75f94ec9d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2304586Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68915}

tools/release/auto_roll.py

@@ -50,6 +50,7 @@ class DetectLastRoll(Step):
       # TODO(machenbach): This should be part or the setdep api of
       # depot_tools.
       Var = lambda var: '%s'
+      Str = lambda s: s
       exec(FileToText(os.path.join(self._options.chromium, "DEPS")))
 
       # The revision rolled last.