[#70264760] Bump govuk_mirrorer to 1.3.1
[#70264760] Bump govuk_mirrorer to 1.3.1

This is because a recent change meant that the GovukMirrorer::VERSION
constant wasn't being picked up correctly causing the job to error.
This patch version fixes that ordering issue.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet