Optional. Default `[]`. When set to an array of arbitrary tag-like strings, builds of this job and other jobs referencing the same tags will be serialized.

This can be used to ensure that certain jobs do not run at the same time, like so:

    jobs:
    - name: job-a
      serial_groups: [some-tag]
    - name: job-b
      serial_groups: [some-tag, some-other-tag]
    - name: job-c
      serial_groups: [some-other-tag]

In this example, `job-a` and `job-c` can run concurrently, but neither job can run builds at the same time as `job-b`.

The builds are executed in their order of creation, across all jobs with common tags.