[CI] ubuntu-16.04 isn't available on Azure Pipelines

[asfimport]

Reporter: Kouhei Sutou / @kou
Assignee: Kouhei Sutou / @kou

PRs and other links:

• GitHub Pull Request #11453

_{Note: This issue was originally created as ARROW-14368. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 11453
#11453