[bazel] Fix extension handling in gcs_mirror

For entries with a specified extension (e.g. rust crates), we were
not actually using that extension

Change-Id: I996f97268471f292a40422a25d016cbf7be2bb7e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/744057
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Chris Mumford <cmumford@google.com>
Auto-Submit: Kevin Lubick <kjlubick@google.com>
1 file changed