[Fuchsia] Fix GN isolate map label for castrunner_browsertests.

TBR=jbudorick

Bug: 922635
Change-Id: Ie3d39b4ca2097a9a9e8061092e30394079c85260
Reviewed-on: https://chromium-review.googlesource.com/c/1423674
Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624446}
1 file changed