[infra-sk] Fix broken import path in //infra-sk/themes.scss.
[infra-sk] Fix broken import path in //infra-sk/themes.scss.

Bug: skia:10614
Change-Id: I8433a04d5e293bd8d64426e05386e4620fad8d32
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/458579
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot