build: fix str vs. bytes error in buildserverid

build: fix str vs. bytes error in buildserverid

ERROR: Could not build app org.fdroid.fdroid due to unknown error: Traceback (most recent call last):
  File "/var/lib/jenkins/userContent/reproducible/reproducible_setup_fdroid_build_environment/fdroidserver/build.py", line 1202, in main
    options.onserver, options.refresh):
  File "/var/lib/jenkins/userContent/reproducible/reproducible_setup_fdroid_build_environment/fdroidserver/build.py", line 972, in trybuild
    build_server(app, build, vcs, build_dir, output_dir, log_dir, force)
  File "/var/lib/jenkins/userContent/reproducible/reproducible_setup_fdroid_build_environment/fdroidserver/build.py", line 82, in build_server
    logging.debug(_('Fetched buildserverid from VM: ') + buildserverid)
TypeError: Can't convert 'bytes' object to str implicitly