Add --build_tests_only to the list of default test options for github_job
Add --build_tests_only to the list of default test options for github_job

Build targets are build in another target and unselected targets might
be build if we do not add that tag. Bazel tests include it and rust
need it.

Fixes bazelbuild/rules_rust#3

Change-Id: Idf54f84bf6668f86d5d308041a4ccf3533e4bec3

bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration,bazelbuild/continuous-integration