[infra] fix recipe bug

We shouldn't modify self.m.vars.extra_tokens in the docker flavor.

I noticed this when doing some debugging. It doesn't seem to be causing
any problems currently.

Change-Id: I2239787f8aec8a25a6a26418c633e68840f74e04
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271058
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
1 file changed