fix(busbar-150): put BUSBAR_ADMIN_TOKEN in the env file too

launch.env is built into '-e' args by the docker launcher, so it should have
reached the container - but the box kept failing with the variable unset, on a
run that provably fetched the commit carrying it. The env FILE is the path that
demonstrably reaches the container (it is how BENCH_MOCK_KEY resolves for the
provider credentials), so the variable now goes there as well.

Belt and braces on a variable whose only job is to satisfy 1.5.0's default
admin_auth secret reference. The admin surface is a separate listener the load
generator never calls.

Author: MattJackson

gateways/busbar-150/env

@@ -1,2 +1,3 @@
 BENCH_MOCK_KEY=dummy
 BENCH_BEDROCK_KEY=AKIAMOCKACCESSKEY:mock-secret-access-key
+BUSBAR_ADMIN_TOKEN=bench-admin-token