rename test action in CI

rename test action in CI to remove mention of py version since the action host python version is irrelevant, since the one used for testing is set in viral-core: https://github.com/broadinstitute/viral-core/blob/master/Dockerfile#L30

Author: tomkinsc

.github/workflows/build.yml

@@ -135,7 +135,7 @@ jobs:
           mkdir -p $CACHE_DIR
           github_actions_ci/list-docker-tags.sh | tail -1 | tee $CACHE_DIR/old-docker-tag.txt
 
-  test_py36_in_docker:
+  test_in_docker:
     needs: build_docker
     runs-on: ubuntu-20.04
     env: